QHY8 First light

[Tim]

Having been driven to distraction trying to use the QHY8 with my new GSO, and battling with condenstaion on the chip and nosepiece, I decided last night to swap the OTA for my little WO72.

It still misted over, but 20 mins with a hair dryer and a 2" dew heater sorted it in the end.

I havent had time to read the guide to gain and offset yet, but in retrospect I think I had the settings wrong, especially as the stars saturated very very quickly. Also, when I did a 0.00 second Bias frame, the figure given by Nebulosity2 was around 3500. This was using 42% Gain and 120 Offset. As far as I understand it, the bias figure should be around 1000?????? To get this I had to use 30% Gain, and 30 Offset. But I have no idea if thats the correct way to go about it, gonna read Craig Starks guide later.

At any rate, these pics were taken with 42% gain, and 120 offset. I tried doing flats and bias for them, but the result was horrible, so the edges of the pics are very black with vignetting.

Also, on the M45 pic, please look at the diffraction spikes. You will notice that they dont taper off, but rather split into two. Am I right in thinking that this shows the pic to be slightly out of focus?

M45 = 14 x400 secs, Flame/Horse/Altinak 5 x 600 sec, M42 4 x 600 + mix of shorter exposures for the core. As these are part of my learning curve with this camera, I'd appreciate constructive feedback, so please point out as much as you can that needs looking at.

I'll take a read of the gain/offset article, but am I right in thinking that each QHY8 will have its own sweet setting? That seems to come across from the posts on various forums?

Cheers

TJ

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[Psychobilly]

Nice set of firstlight Images TJ especially with the QHY8's foibles to sort out...

Still cant believe you have "deserted" the DSLR camp though

Billy...

[Tim]

No, when its all running right, the dslr will be in tandem with the qhy8, on its own WO66.

Another question please, On m45 especially, check the stars near the edges with spikes, you will notice that they have definite two spikes to each side, thus indicating being out of focus. WOuld this be an issue with the spacing? The required gap to my WO field flattener is 56mm. I took the QHY8 chip to nosepice filter to be 21mm, and added 35mm of spacing, including CLS filter. Any ideas?

Thanks

TJ

[narrowbandpaul]

one thing that annoys me, and its nothing to do with you TJ, its more of a quibble, its that use of gain expressed as a percentage. Its a meaningless number, a percentage...

why can QHY express it as e-/DN, or uV/e- if its the preamp gain....

why the need for a percentage...

there is a theory that setting the gain equal to the read noise is advantageous, as it will minimise the impact of quantizing noise, but thats only worth 2/7ths of a DN.

It should be set so that full well occurs at roughly 65000 DN..this may be easiest through photon transfer, but as a rough guide use...

K=full well/65000

assuming that when they say gain, they actually mean gain, ie the gain of the ADC K_adc(e-/DN), i feel they mean output amplifier sensitivity, which has units of uV/e-

might take some trial and error TJ, but you'll get there

Paul

[Tim]

Well I have a loathing for figures and numbers, so dont look at me

On Nebulosity, you select the gain using a figure of 1-63. This is then translated as a percentage. So 27 gain translates as 42%.

I dont really want to understand whats going on, I just want to figure out what seeing to use. Once I find that point, will it remain the same?

[narrowbandpaul]

i expect it will do...at least for the most part...

[Psychobilly]

When I check the field flatness of the Megrez72 and WO FF III with a DSLR it wasn't bad but far from perfect.. (about 13%) at the edges IIRC .

The thing is theres no way of easily adjusting the spacing as its straight to the T adaptor and onto the DSLR and its supposed to be at the perfect distance......The FF III is supposed to work for the range Megrez scopes but it cant be optimised for all of them surely?

I have tought about having some 0.25mm thick stainless steel shimms cut to try between the FF and the T mount and if this goes the wrong way butchering a t-mount to reduce the distance...

Billy...

[steppenwolf]

Excellent first lights - well done!

[Tim]

Have since found out (rtfm!) that I'd saved the FITs as Quick mode RGB instead of RAW as well, so I still have no real idea of a "proper" image from this camera

And another problem, although the gap from chip to focal reducer was as suggested, when I dropped an image from last night into ccdinspector, it gives a curvature of 39.5% !! Any ideas what the issue might be there ??

[RobH]

Hello TJ.

Those are great first light images!

Interesting that you've been running into the dewing problems that many report. I've actually been put off buying a QHY8 because of this...the images captured that I've seen have been great but I can imagine getting rather frustrated with it!

Regarding the diffraction spikes, I've had a very close look ay your M45 nad it looks very well focussed. The small stars are pin sharp and the detail in the nebulousity seems very crisp.

If your spider vanes are not exactly at 90 ( 180 ) degrees to each other, this will have the same effect.

Cheers

Rob

[Psychobilly]

I'm confused now weren't they taken with the WO72? and the diffraction spikes coming from some stretched wires...?

Billy...

[narrowbandpaul]

hopefully the dewing problem is fixed with the qhy8 pro.

[Tim]

Thats interesting Rob. The wires for the front are simply aluminium welding rods glued together, definetly not guaranteed to be 90 degrees apart. I removed them for the m42 shot.

Once the dew was "fixed", it stayed fixed, and im hoping that by leaving the stuff all setup, it wont happen again. Possibly the answer would be to get the nosepiece and filters all warmed up with the dew heater before firing up the cooling. The TEC works so well and dramatically that it chills the glass and housings very quickly indeed. Others use the heat from the camera itself to keep the attachments warm.

The QHY8 is definetly not something you can just use straight out of the box with no considerations.

Im gonna now read up on ccdinspector to see how to make the most of all the spacings etc etc etc......

[Beyond_Vision]

I know how you feel Tim, last spring I was pulling my hair out with my QHY8. I had my DSLR set up sussed out perfectly then all was thrown up in the air when I tried the QHY8 for the first time. The spacing given should be correct did you add a LP filter to your imaging train if so you will need to compensate for that.

I tend to leave the gain and offset at 50 and 115 and never bother fiddling around with it. Is it possible to orientate the camera so it faces down by rotating the tube in its rings? This may alleviate dewing.

The picture are looking promising but look clipped so try upping the offset.

Persevere with it and it will fall into place.

Good luck

Regards

Kevin

[Tim]

yes Kevin, there IS a CLS filter in the train, but the length of the spacer takes account of that, unless, like with a dslr, adding glass alters the focal point????????? but how on earth would you adjust for that?????????

If I plonk all the frames I took last night into CCDinspector, they produce a curve that looks like a parachute, something like 63% curve. What to do? The only thing I can think of is to play around with the spacing and do a live update in CCDIns. and try and get it flatter? Unless the WO72 doesnt need or rather, is better without a focal reducer when using a large CCD??? Seemed ok with the dslr though.

I just may do that with the OTA. From reading Craig Starks guide, it should be possible to readily find the optimal setting for gain and offset. I just havent had a chance to do the daylight test because of all the rain.

TJ

[Beyond_Vision]

I dont know whats going on with the WO FF/FR. I am using a Televue TRF2008 0.8 FF/FR which als requires a 56mm spacing and now with the correct spacing the star shapes are pretty good. I have just downloaded CCD inspector will give it a whirl when I get chance.

Did you run it on a single frame or the stacked image?

Regards

Kevin

[Beyond_Vision]

I have just had a good look at all three images and cannot see anything wrong with the star shapes at all. Are the images cropped if not then I cant believe the figures you are getting in CCD Inspector

Regards

Kevin

[bern]

Hi Tim,

Settings for gain and offset are established for each QHY8 and listed on the quick start guide, try these first.

The dew heater around the nosepiece works very well and is recommended in my tips sheet if you experience misting problems.

CCDInspector can give strange results if the settings aren't right or there is any trailing, others have more experience with this and can perhaps shed more light?

bern

[narrowbandpaul]

bern, are the dewing problems fixed with the QHY8pro, and what other differences are there over the QHY8...

cheers

paul

[Eddie]

hopefully the dewing problem is fixed with the qhy8 pro.

I never had any problems with my Standard QHY8. I have had more problems with my Art11K

Bern is indeed right on CCD inspector you need to use a short exposure (to avoid guiding errors) and a single frame.

Eddie

[Tim]

i'll go take a look at the short exposure taken for Orions core, 1 sec....... And yes Kev, they are cropped to about half size, I'll post a full size m45 for comparison.

Dropping individual short exposures into CCDIns. is giving varying results. There is NO trailing! That much I have cracked at last!! (Drift aligned for two hours). One short exposure gives a result of 19% curve, and another 35%.

[Tim]

Here is the full field view.

The stars with double diffraction spikes ie. out of focus are clearly seen at the edges, I highlighted one but the rest are obvious.

the question is, can I expect to improve that on the WO combination? Should those stars be sharp to the edge, or do I expect too much from this little unit?

Thanks Bern, i'll take another look at those. I did try those settings at first with Maxim, but I got so frustarted with that program that I bumped for nebulosity, at least until i know my way around the camera a bit better. Nebulosity is a doddle to use, but has the high end features too it seems. And its cheap

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[Tim]

Hmm, another artifact I have noticed, is a pair of parallel lines on the right of the image. They are on every frame, including flats, but I cant see them on the 0.00sec bias frames Anyone else get that?

[Eddie]

Could be poor coli and / or in-correct spacing from the coma corrector.

Eddie

[Tim]

But how would you collimate a WO72? All fittings etc were as tight as could be, and the spacing was the suggested 56mm, as best as I could tell. I guess i'll go 1mm either side of where it is to see if that helps.