Light box too bright for ST8300

[mickw]

Why not just get a pack of resistors from Maplin and experiment

Or

Chris's ND film

[Mike]

Why can't they be dimmed?

It an assumption I'd admit, I'm basing this on a LED needing a minimum voltage to fire I'm not sure what the voltage range is for this type of LED, maybe I'm being too pessimistic.

I've yet to come across an LED that can't be dimmed. If they couldn't LED TV's wouldn't be much use as pixel brightness is essential for it to work.

As Mac says, PWM is just turning them on and off for a duty cycle anyway. It is just so fast it deceives your eye (and if fast enough, your camera too) into thinking it's not so bright.

[mickw]

LED dimmers
This company could help, you can also find them on ebay

http://www.myled.com/led-accessories.html?cat=236

[MarkS]

That's a lot cheaper than Maplin!

[Mike]

Pretty much anywhere is cheaper than Maplin.

[Ivor]

I had a 100K pot at home and tried this and it appears to work in principle but because it was too big it didn't give me the sensitivity I needed so I've got a 1K to try out instead.

This process has been postponed as the flats I produced highlighted the bigger problem was with the ST8300. My subs have been coming out like this for a while and I could work out why.



Well to keep a long story short it appears the ST8300 can suffer from condensation inside the CCD chamber, there is a desiccant pack which is inside the camera casing which should last about a year (which explains why the problem started to appear last April) which you have to drying out in the oven @ 170 for 4 hours! Also SBIG will send you a heater strip for free which can be soldered into the camera.

So I now have to cook a roast dinner for the family so I can get the camera working again and I'm waiting for SBIG to send the strip through.

Once the desiccant pack is reset I'm going to open up the camera and see if I can clean the glass screen in front the of the CCD.

I'm hoping to get the strip this month as I was planning on going to the Nov uDSC, but I'll have to wait and see.

[Mike]

Always make sure you store your camera somewhere at ambient temperature. Don't store it in the warm indoors. Keep it in a shed or garage.

When cooling the camera make sure you do a stepped cool down process, don't just go straight to the set point temperature. E.g. let it cool to -10, wait 5 mins, then down to -20, wait 5 mins, then down to -25, etc. If your camera has a warm up feature and the software will allow you to use it then always warm up the camera prior to turning it off. All the above will minimise the chances of it reappearing. Rapid cooling from a warm camera and rapid heating up again afterwards are a sure fire way of getting condensation inside no matter how well it is sealed. Keeping the camera indoors and then taking it out into the cold and cooling it to well below zero rapidly would be main culprit of this. Same as bringing a cool camera into a warm house afterwards. Bad idea.

[MarkS]

you have to drying out in the oven @ 170 for 4 hours!

On that note, knowing that gas produces lots of water as it burns, I've often wondered how much higher the humidity is in a gas oven (compared with electric) and does it matter when drying out dessicants. 

[Mike]

For desiccant bags I always find the best place is to leave it in an airing cupboard for a few days. No moisture in there.

[Ivor]

Alas I don't have an airing cupboard, but I do have an electric oven. Mark's comment does make me think doing this with the roast won't be a good idea as it will add moisture to the environment.

[Carole]

I put my dessicant on the radiator to dry out.  Also keep my camera in a plastic box with extra bags of dessicant.  

Regarding the light box, can you not put pieces of paper in front of the light source to dim it?  

Carole

[Ivor]

Yes I can Carole, however it needs further experiementation with the smaller pot to decide whether it would be better to place the paper in front of behind the diffuser or even at a distance from the diffuser. I also want to experiment with some sticky back plastic to aid easy removal of dirt from the paper.

It's still in a prototype phase but I can post up some pictures if you are interested. I'm planning to do a tutorial for this once I've ironned out the issues. The current design should be able work with any scope up to 25cm, bigger scopes could be accommodated with a large selection box .

[mickw]

Look here
http://forum.orpington-astronomy.org.uk/index.php?topic=9376.0

[Fay]

cant you just buy a flat panel & put sheets of paper under it

[Ivor]

Look here
http://forum.orpington-astronomy.org.uk/index.php?topic=9376.0

Looks interesting i guess it depends on the size of the resistor inside on whether it is viable. I'll be interested in how others get on with them as it is certainly a cheap altnerative to a dewheater.

cant you just buy a flat panel & put sheets of paper under it

A flat panel costs at least £60, my solution cost less than a tennor, I got to be manly with a soldering iron and eat a tub celebrations. When you look at the choices there's only one worth picking