Strange streaking stars on outer edge of my pictures

[samir_ansari]

Hi everyone,

last night was my first light with my new QHY9 and while I am over the moon of the smoothness and quality of the image I am not so happy about the weird stars I am getting all around the edge of the picture:

Now the thing is I don't actually remember travelling at warp speed while taking these pictures but the photos suggest otherwise...

I am using a skywatcher focal reducer/flattener and always have been with my old camera and never had this problem - anybody have any ideas on what this could be?

Thanks,

Samir

[Stephen]

Looks like curvature/flatness issues to me - does the new camera have the same back focus distance as the old one?

You may need additional spacing between the camera and the flattener?

[Stephen]

To clarify a bit, if the "old camera" was the 450D - then you would of needed no spacing as the 450D + T-ring would of been 55mm.

The QHY9 has 17mm (check this, I may be off a bit) meaning you will need a further 38mm (minus any other items in the chain such as filter wheels) of spacing (t-ring extension tubes) between the camera and the flattener.

[samir_ansari]

Thanks Kh3ldar, I think you are right. I am just in the process of finding the dimensions for the filterwheel as the back focus of the QHY9 (including glass window) is 27mm.

As I'm using a nose piece with the filterwheel I'm quite worried that I've gone over 55mm on the spacing but I'll have to check. Where's my ruler!

[Stephen]

Thanks Kh3ldar, I think you are right. I am just in the process of finding the dimensions for the filterwheel as the back focus of the QHY9 (including glass window) is 27mm.

Great

I put a tooth pick through mine and marked both sides then measured the distance

Also although I would love expensive adjustable Baader extension tubes, you can get all sorts of fixed size tubes dirt cheap off Astroboot.

You can also get small delrin spacing rings from FLO for about £8 (for a set) I think - handy for adding that additional 1mm or so you may find yourself short.

[samir_ansari]

Hmm, according to these two schematics:

http://qhyccd.com/ccdbbs/index.php?PHPSESSID=0e3b628edfddbf90a7b1ae4755d57120&action=dlattach;topic=1751.0;id=2011;image

http://tienda.lunatico.es/WebRoot/Store/Shops/Store_002E_Lunatico/MediaGallery/QHY/RuedaPortafiltrosLunaticoMedidas-v2.jpg

my distance from the reducer is a whopping 80.7mm The problem is I need the nosepiece because I am screwing a light pollution filter into it and according to the dimensions even if I get rid of that it would still be 56.3mm

[spaceboy]

This is very interesting. Being a new fish to imaging I thought fraks were free from the spoils of warped stars. So I take it ...coma correctors for newts and flattener's for fraks ???

[Stephen]

I'm afraid this is where the fun starts I'll defer this to someone using the same setup.

I would suggest though, if you are using LRGB, you don't need the LP filter?

56mm might be close enough - you would need to test it.

After that, you might have to look for a slimmer M54 to T, slimmer filter wheel, or slimmer camera adaptor that doesn't add that additional 12mm on?

[Stephen]

This is very interesting. Being a new fish to imaging I thought fraks were free from the spoils of warped stars. So I take it ...coma correctors for newts and flattener's for fraks ???

Bang on!

[steppenwolf]

So I take it ...coma correctors for newts and flattener's for fraks ???

That's the bottom line!

[samir_ansari]

I would suggest though, if you are using LRGB, you don't need the LP filter?

The QHY filters I have do have a notch in the transmission lines to combat most of the light pollution however I live smack-bang in the center of London and I need much more help with the fight than most.

As much as I probably live in one of the worst places in the galaxy to take up this hobby I believe that's also part of the fun

[Stephen]

The QHY filters I have do have a notch in the transmission lines to combat most of the light pollution however I live smack-bang in the center of London and I need much more help with the fight than most.

As much as I probably live in one of the worst places in the galaxy to take up this hobby I believe that's also part of the fun

Ah I see

There's always a sneaky way that I use ......

ScopeStuff

I use it on my ST80 (which uses a DSIc for guiding) which only uses T-thread connections (rigid.)

You essentially sandwich the 1.25" filter in between any T-thread to T-thread connection

[samir_ansari]

Very sneaky indeed! however I should have mentioned I am using 2" filters.

Normally I would just go and ask the manufacturers about this but the QHY customer service is absolutely shocking. Please do let me know if you hear of anyone who has a similar setup to me because I'm sure others have found a way around this.

If all else fails I suppose I could just only use the focal reducer when I am doing single filter narrowband sessions and whenever I want to do a bit of LRGB I could just lose the reducer altogether - although this would not be ideal .

[Stephen]

Does this help any? Moves the filter to the other side I'm guessing?

First Light Optics - FLO Adapter for Skywatcher Focal Reducers

[samir_ansari]

Ah ha! I think that's exactly what I need.

With the nosepiece moved infront of the reducer I will end up with a distance of around 50.8mm from the chip with the need to only use a 5mm spacer. Thanks so much for the help with all this!

[Stephen]

No worries, can't wait to see the results

[martin_h]

Ah ha! I think that's exactly what I need.

With the nosepiece moved infront of the reducer I will end up with a distance of around 50.8mm from the chip with the need to only use a 5mm spacer. Thanks so much for the help with all this!

As per my PM that is what I use...BUT I drilled and tapped a 3rd hole and made the other 2 bigger in the drawtube holder....those tiddly thumbscrews just dont do the trick and all the gubbins behind just droops.

EDIT: Take a look at this thread.......... http://stargazerslounge.com/discussions-cameras/158880-how-fit-lp-filter-sw-reducer-flattener.html

[samir_ansari]

Thanks for that Martin, that's a great idea. I've had countless Mr Bean moments so far when imaging and can't really afford another one.

[Catanonia]

Some numbers for you.

The CCD is actually 20mm from the face of the QHY9. Remeber the CCD is under a glass window and is actually deeper than you think.

The filter wheel is 18mm wide and don't forget a few mm for the adapter connecting them both.

Take a look at this picture of mine and the adapters. The QHY9 can be a pain in the butt and I had to remove the filter wheel cover to get things working.

This is with a ATA reducer attached and not your reducer / corrector.

With all my messing around the smallest number I can get is 65mm which is bang on perfect for my corrector. If I removed the OAG then I could gain another 9 - 10mm so this setup might work for you.

As said, with the QHY LRGB filters, you shouldn't need the LP filter.

[samir_ansari]

Thanks very much for that Catatonia, it's really cleared a few things up for me. However just to be clear do you mean the CCD is 20mm to the closest outside face or that it's 20mm to the surface of the optional glass housing?

Also in regards to the LP filter I believe I do need it as this is the spectral response graph for the QHY blue filter:

This unfortunately doesn't cut out any of the light pollution between 400 and 450nm

[Catanonia]

20mm from ccd actual chip surface to flush of the qhy camera front without the filter adapter. So roughly from ccd to end off filter wheel flush is 40mm

As for LP the only way to know for sure is to try it

[samir_ansari]

Ah ok - I remember reading somewhere that without the glass cover the TEC isn't quite as efficient at cooling down the CCD. Have you come across this yet or is that just a load of tosh?

Also how thick is the Baader M58 to T2 adaptor?

[Catanonia]

I assume you mean the glass housing inside the camera covering the ccd? I always keep it in place as it has a heating element to warm the ccd after use to prevent dewing.

The adapter is about 4mm and converts the filter to a T2 thread.

[samir_ansari]

Sorry I meant the one sticks out of the camera (in the pic below). It can be unscrewed easily but when I received it from Bern it was already fitted.

In your photo it looks like you already removed it, or perhaps this is a new thing they are shipping out with QHY9's?

[Catanonia]

I have never used it. All it does is add length and so I removed mine from day 1

I think it's reason is to keep the unit sealed and prevent moisture.

Just remember than when you are finished after a season, gentle warm up the ccd with the ccd warmer functionality. This will stop moisture forming on the ccd via rapidly warming air.

Also get used to taking the qhy9 apart, I regularly take mine apart to clean.