What is happening here?

[myk68]

Hi all

You know the old adage 'Don't fix what ain't broken'

Wellllll .....

I've had the chance of a QHY8 so have changed my set up around. the 314L+ is now on the C8 and the QHY8 is on the 80ED. Did not expect the rather great increase in exposure time, the QHY8 seems so less sensitive than the 314L. any way thats maybe another post.

The issue I found last night was this, with the 314L on the C8

Now I had to set the camera up as in the next image as this was the only position I could get it to focus. I have a Meade FR 3.3 on the back on the C8, then a 10mm and a 15mm adapter, a 1mm perspex washer(otherwise the adapter stops the filter wheel from rotating), then the Atik filter wheel and finally the 314L

Im guessing I need a different spacing or something, or is it a field flattener.?? I used to have this as my guide scope with the IC16 and never noticed this effect.

Ideas anyone?

cheers

Mike

[rfdesigner]

yup flattener spacing looks way off.. mega-coma like that makes me think the FF either way off.. back to front.. or actually working against you (wrong for scope) I take it the you've had the FF working correctly with the 314?

Derek

[myk68]

Hi Derek

its a long time since I have had the 314L on the C8 so couldnt say for sure. I seem to remember I got it working fine without the FR,but the field of view is small as you would expect, and I thought I had had it working with it too but this may have been with the wheel off and may still have had the issue.

Is there nothing I can do to resolve it?? am I trying to 'widen' the view for my C8 to much?

mike

[Oddsocks]

Hi Mike,

The MEADE spec for optimal back focus distance for the 3.3 FR/FF is 45mm (from the MEADE website).

William.

[steppenwolf]

That's about the worst case of coma I've ever seen but that doesn't help you solve the problem!! I agree that the spacing seems well off and a x3.3 focal reducer is quite a severe beastie so spacing will be very important. I'm surprised to hear that there isn't enough focus movement to accommodate the correct spacing though as SCT have this in spade loads.

[ollypenrice]

I very much doubt that you can use the 3.3 on anything other than a webcam sized sensor. It dates back to the dawn of CCD imaging when all mainstream CCDs were tiny and the SCT makers came up with this as a way of relieving the problem. As I've said before, if all you had to do to have an F3.3 astrograph was buy an SCT and a 3.3 reducer then it would be the only imaging scope any of us would ever use! In truth I can only think of one member using it and that is, indeed, with a tiny chip.

Olly

[ollypenrice]

For more gloom on the image circle of the 3.3 have a glance at this; http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4881447/Main/4871646

Many dealers do warn that the 3.3 is a small sensor accessory but some don't and this is very bad.

Olly

[myk68]

First of all thank you for the input all.

Olly, I know you know your stuff so thank you for that explaination, it makes sense. I also would go with this as the centre of the image does look 'perfect', its the surrounding area that doesnt seem to fit.

I take it from this that Williams back focus of 45mm will make very if any difference. Therefore REMOVE IT seems to be the only option.

I always wondered why you needed an astrograph or some other equipment when I just had a 3.3 reducer. Ah well another step up that learning curve(cliff) lol

Mike