Maximum CCD Sensor size for 1.25" filters.

[ribuck]

Hi All,

I would to get an idea on what people thin is the maxium ccd array size that can be used with 1.25" filters.

I'm quite interested in the new QHY 9, which is described at being close to the limit of using 1.25" accessories.

Is anyone using this ccd with 1.25" setup ?

In particular, i'm interested in understanding what sort of edge of field distortion i would see uing this ccd with a 8" reflector @ F5(1000mm)

Rich.

[Merlin66]

To answer the first question, we'd need to know how far the filter would be from the CCD chip and the f ratio of the scope; you can then easily calculate the un-vignetted field size. ie if the filter was sitting hard on the CCD then the field would be the 28mm diamter or so clear aperture of the filter.....

[NickH]

In practice, a KAF4021 works (just) on a 1.25 inch filter wheel, at around F7.4 using my ED80, miniscule cropping right at the very corners..

[ribuck]

So nick, on a F5 (1000mm F/L), do you think this will be ok ? I've heard that using this size ccd with 1.25 filters will work but would cause serious Vingnetting (Excuse Spelling).

[Eddie]

The QHY9 with a 1.25" filter will be fine and will cause minimal vignetting.

I have done an illustration of the various ones bought up here against my Art11002 (with a KAF11002 sensor and mounted 2" filters and this causes more vignetting than the QHY9 would (this is based on Astronomik filters, if you want other filter makes let me know)

Eddie

[Merlin66]

Eddie,

What distance from filter to CCD???

[Eddie]

These illustrations assume the filter is flush to the sensor.

Eddie

[steve51450]

the qsi540 uses this chip and is fine down to f4 with 1.25 filters as it has an internal filter wheel and the filters are very close to the font of the ccd chip, you get minimal vignetting even down to f3.5 i think

[ribuck]

I emailed QHY support about this last week but unfortunately no answer, as yet. I'm hoping i can get away with 1.25, as i dont want to have to spend another £600+ replacing filters with 2" ones.

[Eddie]

You will be able to use a 1.25" any vignetting you get will be minimal and easily calibrated out using flats or artificial flats or the lens correction tool in photoshop.

Eddie

[ribuck]

Sounds like i best start saving then, and hope the £picks up to bring the price down.

The wierd thing is that i posted the question on the QHY forum and people on there reckon that at least 50% of the image would suffer from vignetting, which seemed a little high.

I'mm maybe see if i can get qhy to post an image using 1.25" filters.

[Eddie]

50%!!! That is complete nonesense!! You would have to do some pretty extreme stretches on the image to get such bad vignetting!

Eddie

[ribuck]

I emailed the camera designer directly asking him to post some images ysing 1.25" filter as piece of mind. Hopefully he will be accomodating.