Cooling a DSLR

[MarkS]

easy enought just slide your telescope forward when it attached to shift the center of gravity.

I don't think CoG is the problem.  With all that extra weight, focuser droop is more likely.

Mark

[Carole]

I don't think CoG is the problem.  With all that extra weight, focuser droop is more likely.

That's more along the lines that I was thinking.

Carole

[Carole]

Well it's arrived VERY quick service from Germany.  Ordered Monday arived today.

Have put it all together, I think it will be OK weight wise, but a few snags.

The hole at the front is not big enough the accommodate the field flattener and can only get the DSLR onto the drawtube using a 2" extension piece    so will either have to enlarge the hole or get a new FF (which could be on the cards anyway but an expense I wasn't wanting just yet) so bit of a quandry.

If I enlarge the hole to fit current FF this could be too big for a new FF (on the other hand it might not).  
No way to change the battery without dismantling the whole thing, so might have to get an electric "battery".

What would happen to the images without the field flattener, I've never tried it?  I guess a coma or something.

Carole

[Rocket Pooch]

well its at this point I think your all nuts going down this route, I guess its something like £200 for the cooler and £300 for the DSLR ignoring all the bits, surely a basic cooled one shot colour camera for an extra £300 would have been the way to go, you would have 16bit DAC and also proper cooling and no issued with weight, focal reducers and a better QE.

But then again, if there was one perfect system we would all have it?

[Carole]

You're probably right Chris, but I already had the DSLR, was used to how it all worked etc etc.  Various people have been trying to talk me out of getting a one shot colour CCD which I was definitely considering.  Then you get to a point where it is a bit late to turn back. 

Carole

[Rocket Pooch]

Hi,

It's a shame really I have seen some images from Olly's one and although the noise is a lot higher and the sensitivity less than the QSI it's still a lot better than the DSLR test done at his place.

Maybe Mark or Robert will be the 1st!

Chris

[RobertM]

I agree with Chris, it sounds like a whole heap of trouble to me.

Since I can't afford one of these: http://www.centralds.net/en/index.htm

For me the next step would be a cooled APS chipped OSC.

Robert

[MarkS]

In my opinion there is a still gap in the market for a good OSC.  The popular KAF 8300 is simply the wrong chip - the read noise is too high and the sensitivity is too low.  It simply doesn't represent a decent enough upgrade from a £300 DIY modified Canon DSLR.  When a multimegapixel OSC is produced with high sensitivity and low read noise then I might be tempted.  For instance a scaled up version of the Sony HAD chip they used in the old Atiks would be a killer camera.

So instead I spent my 3 grand on very-fast very well-corrected optics and I have never regretted that decision.  You can do the same - there's a Bananascope on fleabay at this very moment.

The point you are making is a good one though - if you end up spending hundreds followed by hundreds followed by hundreds of pounds on a DSLR then maybe you should have bought a OSC in the first place.

Mark

[Rocket Pooch]

Hi,

Who said the 8300 chip?  All I was saying is there has to be a point where a DSLR just will not hack it and the mods are pointless.

Do you also really think the QSI8300 camera spec is worse than a DSLR, produces more noise and is really less sensitive? 

In my opinion I'd stick with a F5.6 120 refractor and a cooled OSC CCD and not square stars of an Epsilon any day and probably save £1,000 in the process   But each to thier own I guess?

But I'm a mono man so who cares

Chris

[Rocket Pooch]

Since I can't afford one of these: http://www.centralds.net/en/index.htm

Again that would make a right mess of the diffraction spikes on your hyperstar   Boy would it also look silly at weddings.

[RobertM]

but it would keep the corrector dew free

[Rocket Pooch]

Now there's a positive for it

And just to highjack the thread a little, I've been reading about optical designs and F Ratio's, its quite interesting to see how inefficient Newt's with correctors are, for example (these are not actual numbers) but;

A new say 8" F4 800mm with a large central obstruction does not let through all the 8" worth of light, say equiv of 8" at F4.5, then if you deduct the efficiency of the mirror coatings typicall 87% you lose another 26% of the light comming in, thats F5 perhaps, your not far off an ED120 with a flattener @ F5.6 x 120mm =  672mm which lets in 96% of the light.  Interesting eh!  Craig Stark has written loads about it, its all good.

The problem is bang for buck, an 8" F4 @ 800mm performing as it does is still a lot cheaper than a 6" F7.5 APO like a lot cheaper.

His articles on resolution are really good and backs up Marks comments about up sampling a bit, that is until you get 1" seeing, which we don't get at all.

Chris

[mickw]

there's a Bananascope on fleabay at this very moment.

We may know the seller 

[MarkS]

Do you also really think the QSI8300 camera spec is worse than a DSLR, produces more noise and is really less sensitive? 

Not at all.  It is undoubtedly a definite improvement over a DSLR (apart from the read noise).  But for me, not enough to justify the price jump from £300.  But I do think there is a gap for a much better chip than the KAF8300  at that price point and that will make it worth jumping.

We may know the seller 

No - not me!

Mark

[mickw]

No - not me!

Agreed, Robert may also know him - The plot thickens