Light path lengths & Problems with focus

[Mac]

I spent about two hours today setting everything up in daylight and having a play with my new F3.3 reducer.

My F3.3 reducer consists of the following

F3.3 Lens and 3 separate length tubes, which when connected together make up the F3.3,

with just the lens and no extension tubes it is F5, plus various combinations inbetween.

To start with I set the scope up as follows.

Scope - F3.3 reducer - H9.

had a nice play and got to grips with focusing, ect, no problems, light path was square, ect,ect, and quite a nicce field of view.

I then wanted to add the focuser and filter wheel.

Scope - F3.3 reducer - Focuser - filter wheel - H9.

As the focuser and filter wheel were aditional lengths, i removed the extra extension tubes.

The problem is the length of the focuser and filter wheel, is about 1cm longer then the extension tubes

I now have the following problems.

The H9 is now behind the focus point of the reducer, and i am unable to focus the H9 at all.

From full travel end to end of the scope, i am unable to achieve focus.

Idealy i want to keep the focuser as it allows me to focus the image without mirror shift.

Which set up would be better?

1) scope - Focuser - F3.3 - Filter wheel - H9.

2) scope - Focuser - Filter wheel - F3.3 - H9

3) scope - Filter wheel - F3.3 - Focuser - H9

Assuming i have the various adapters.

My only worry is the filter wheel, as the amount of thread is tiny, and dosent look like it would support a huge amount of weight.

I was thinking of 1 as my best bet, any thoughts or comments, apart from getting another scope

[Rocket Pooch]

Hi,

If its on the 200R take the focusor out all together and test it with the normal focus, it will work then.  Then try the focuser, one small point though, again as with another posting here, I don;t think the light cone will cover the chip evenly.

If you need a SCT to 2" adaptor you can morrow mine to give is a go, also are you using the normal nose for the H9 or have you got a T-T mount male to male to get it bang up against the filter wheel?

Lastly check the focus point of the reducer, its 4" in my AP from the front element of the reducer to the chip, you should be able to find this somewere, this will give you the measurement guide you will need.

Ramble ramble...

Chris

[Mac]

I've got the male - male Mount so its bang against the filter wheel..

If i remove the focuser and filter wheel and replace it with the extension tubes. I can get it to focus without any problems.

The focuser and filter wheel is about 1cm longer then the Extension tubes, so im assuming its pushing the H9 past the focus point.

I can only asume the light paths are something like this.



The top one allowing me to move the H9 in to focus, ect.

The bottom one, because the H9 is now further behind the point of focus, i am unable to bring the H9 close enough, to achieve focus.

I was just wondering if by placing the F3.3 after the focuser would it cause any problems? as the reducer itself is now moving?

so although the light would be able to be brought to focus, would the image size shift?

I supose the only real way to find out is to have a play during daylight and try it.

[RobertM]

Mac, If this is a 200R then the 3.3 reducer will overcorrect the corrected optics.  The main advantages of the AP reducer that Chris mentioned are that it is a pure reducer (no correction) and you can screw it directly (via spacers) to the filter wheel.  Since it's designed to fit inside a 2" focuser it travels in and out with the image train.  I found the SCT thread Celestron reducer corrector was causing vignetting with the H9 which will be worse with the 3.3.   If I wanted to change the reducer before I had to dismantle the image train and the JMI focuser to get the reducer off, now I just release the 2" clap screws and unscrew it from the nose piece.

Moonlight do make a special focuser for doing what you want and it places the RC inside the focus assembly where it moves with the drawtube (only fits the larger sct thread I think).

[JohnP]

Mac - when did you get an H9?

[Rocket Pooch]

get with it john

[JohnP]

OK - I've just looked back at the old threads... He never actually said he had got one.... Geeezzzz...!!!!

Look mate I'm getting old the memory starts to go...

John

[Mac]

Look mate I'm getting old the memory starts to go...

Your memorys fine.

I got my Starlight Xpress SXVF-H9 CCD Camera last week.

Spent all night effing and blinding, so decided to set it up during the day,
dam site easier, i must say.

My scope is just the old LX200 GPS, so the F3.3 wont over corect the optics, in  fact it should give me a nice flat field.

BUT. If i use the focuser to move the F3.3 and eveything else, then the size of the image will change, as the reducer is actually being moved as well.

So i have a choice of either not using the filter wheel, or not using the electric focuser, and rely on using the main mirror focus.

By the way, your memorys fine 

[JohnP]

Did u get it new or used? I think i'm at the stage where I need something with a larger chip.. What are you using for a guide camera?

John

[Mac]

I got it new, as its the F version,
As for guiding, err, nothing at the moment,

I did get the 300mm lens to use as a guide scope, but im still looking for my toucam.

But i've ordered an adapter for my nikon lens's to H9
so hopefully i will be able to do some super wide field.

I also got a set of narrow band filters.
Ha
Hb
Oiii
Sii
Clear
and light pol.

So when its all up and running i hope to get some good images.

Fingers crossed.

[RobertM]

Sounds like a good combo Mac, looking forward to some great images.  Which Filter wheel did you get ?

[Mac]

Which Filter wheel did you get ?

I bought the True Tech super slim wheel.
http://www.iankingimaging.com/show_product.php?id=171

With the 7 slot filter wheel, including dark position.

So i can use the clear (ir uv) filter for quick focus,
and then more selectively focus in each of the Ha Hb ect.
plus Loight pol for the luminance.

Although unless im doing 10 min + subs, I wont actually need a dark frame, as the H9F has such a low noise factor.

The SXV-H9 is a 1392 x 1040 pixel high resolution CCD camera that provides truly world class performance.
It features a Sony ExView CCD that has such low noise levels dark frames are rarely required.

The download speed from the chip is fantastic, Less then 0.6 secs full frame, and a binned 4*4 is <.1 secs. so focusing should be a lot quicker

Mac.

[Mike]

The download speed from the chip is fantastic, Less then 0.6 secs full frame, and a binned 4*4 is <.1 secs. so focusing should be a lot quicker

You're lucky, you've got the newer version. It takes a few seconds on my version of the H9. 

[RobertM]

Mac,  That's great, mine takes about 4-5 seconds for a full frame download.  Also I've found that darks are unnecessary even with 20 min subs but bias do take out a fair amount of the residual background noise (not that there is much).  I find the difference between an average bias and a 10 minute dark is around 50-70ADU, if you're a purest or have really dark skies then fine but for the effort it doesn't really seem worth it around here.  The SupaSlim is one I've been looking at too, the main advantage is for a quick change of filters, the SBIG I have is like the Atik - held together by Allen screws.

[JohnP]

Blimey Mac all I can say is you must be in your mrs's good books if you've been allowed to spend that much on toys....

I can't wait to see the results you get - Looks like you have some great kit. I look forward to welcoming you to the 'club' of autoguiding trial & tribulations....

John

[Mac]

I did have a quick play with maxim and auto guiding with the H9, but as that was only a quick play, i didn't
realy achieve anything, but as i've now found my toucam, im going to have a play with it set up on the nikon lens,
F300m + 2X tele convertor + toucam,

should be around the same focal length as the main scope and the F3.3.

I i'll have to have a go and se what errors i get.
I've also been looking at using software to train the scope for the PEC, which i still need to do,

So if i get the software to do the PEC, i can leave it auto training for about an hour, which should give it plenty to chew on.

I;ve also started to balance the scope, which is giving me weird headaches, but thats for another thread.

Mac.

[JohnP]

Hi Mac,

Not sure but I think you need to be careful when implementing PEC training & autoguiding software together as they can 'fight' against each other & you can endup with worse guiding... I might of course be talking a load of ****ocks......

Any chance you can email me a 5min dark from your H9 - If you could email me the fits file that would be great...

Thks,  John

[Mike]

Not sure but I think you need to be careful when implementing PEC training & autoguiding software together as they can 'fight' against each other & you can endup with worse guiding... I might of course be talking a load of ****ocks......

No that is perfectly correct. Guiding will try to correct movements made by the PEC as they don't talk to each other. When guiding turn PEC off. PEC is to allow longer exposures unguided only.

[JohnP]

Cheers Mike...

[Mac]

I'll make sure then that the PEC is off, as of now.
Thinking about it, I havent actually switched it on.

I dont know how long it takes to cool down, but i'll get it up and running and post a 5 min dark later, any advances on 5 mins.

Acording to the blurb, it will take over 100Hr's to saturate the chip. I'll think i'll take their word for that one.

I'll give you the room temp as well so you can get an idea of the chip temp.

Mac.

[JohnP]

Thks Mac - I'm just interested in seeing how many hot pixels there are.... John

[RobertM]

Mac, could you do a 10min dark so I can compare it with mine.

Cheers
Robert

[Fay]

Wow, Mac, how exciting.

I wish I could help but got lost a few posts back, regarding your equipment setup.
I found there was a lot of testing with additional aids, to all different positions until the correct place was found for everything & it changes depending on what scope etc you are using. I have to think a bit everytime I use a different camera , scope filter wheel or no filter wheel etc etc etc, what to unscrew, add, change around!!!!!! Then the guiding goes wrong!!!!! 

[MarkS]

Mac,

I agree you should use option 1:  scope - Focuser - F3.3 - Filter wheel - H9.

You had the following worry:
"I was just wondering if by placing the F3.3 after the focuser would it cause any problems? as the reducer itself is now moving? so although the light would be able to be brought to focus, would the image size shift?"

I've done a bit of diagrams and maths.  Yes, it is true that when you change the filter, you may have to refocus (glass thickness etc.) but I am confident enough to bet you a pint of beer that the image size remains identical.

Mark

[Mac]

As requested, here are the three dark files

1) 5Mins Fit, after the ccd had been cooling for 20 mins,   http://www.macrhon.co.uk/website/oasphotos/darks/5min.fit
2) another 5 min fit, taken straight after the first one       http://www.macrhon.co.uk/website/oasphotos/darks/5min2.fit
3) 10 Min Fit, again taken straight after the second one.   http://www.macrhon.co.uk/website/oasphotos/darks/10min.fit

havent checked them myself yet,

Just fixinging someones pc and building the nursery. 

Mac.

[Mac]

dont forget to right click and save as, otherwise they will open as text files,

[RobertM]

Your 10 minute dark doesn't look right, I reckon you must have some light leakage or something.

[Rocket Pooch]

There's only 100adu difference in that image, if light got in it would be higher than that.

Mac can you take 32 bias frames and average them and post it up here, I want to see if its readout noise.

[Mac]

Your 10 minute dark doesn't look right, I reckon you must have some light leakage or something

Well i didnt move the ccd at all, it was just sitting there on the box, with the 1 1/4 adapter on, and the rubber cap over the end,

The room temp was probably around 18~20 deg,

and it was taken straight after the two 5 min subs, so if anything they would have the same light leakage.

I'll do another 10 tomorrow, and i'll take the 32 bias subs,

Can i average them in maxim or do i have to use, DSS?

Mac.

[JohnP]

Yep - I checked it in Aip4Win as well & the 5mins show a slighly brighter patch through the middle but like Chris says there is only about 100ADU between the brighter & darker bits.... don't think that would be an issue at all.

The number of hot pixels is very low & there are only one or two saturated (65,000ADU) pixels...

Looks very good to me...

John

[RobertM]

Yes, I checked that last night and it was about a 70 ADU hill across the middle, it just looks worse when it's stretched.  I would still check with SX to make sure this is ok, also ask them what the bias level shoud be.

[Mac]

Here are a few more Fits. for you to chew on.

1) 5 Min
2) and another 5 Min
3) 10 Min
4) Single Bias
5) 30 Bias frames stacked in DSS. (I think 've done this one correctly.

http://www.macrhon.co.uk/website/oasphotos/darks/5mindark.2.1.fit
http://www.macrhon.co.uk/website/oasphotos/darks/5mindark.2.2.fit
http://www.macrhon.co.uk/website/oasphotos/darks/10mindark.2.fit
http://www.macrhon.co.uk/website/oasphotos/darks/BIAS.fit
http://www.macrhon.co.uk/website/oasphotos/darks/ave.fit

[RobertM]

Mac, your Bias average looks suspiciously like it's been converted to colour, size should be the same as the original bias it was made from i.e. abt 2.8Mb

[Mac]

I thought the file was a tad on the large size,
I've had another go, and uploaded the new file, this time it is the correct size.
I think i had the drizzle checked before.