Testing... 3 very brief images..

[AlexN]

In testing my new imaging setup I was able to shoot through some sucker holes in cloud over the past few nights...

3 images, all unguided (still shopping for a guide camera)

NGC 253 (and accompanying globular cluster) 10x60sec exposures, flat corrected but no darks)

NGC 2070/LMC section 10x60sec, flat corrected (horrid gradient from light polution)

M42 30x30s + 30x60s + 30x120s flat corrected.

All at ISO800.
Camera : Self modded 450D (UV/IR filter removed, Anti Aliasing filter removed)
Optics : Tokina 300mm f/2.8 SD
Mount : HEQ5 Pro

Lessons learned from these tests.
1. My Nikon to EOS adapter does not put the camera completely orthagonal with the optics. I am working on some shims at the moment to correct this.

2. At f/2.8, temperature changes of 1°C cause an appreciable shift in focus. I am running an Ardrino based stepper motor focusing system
Credits go to SGL Dome Automation Team, My Uncle Ken (Nico13) and the world wide web for all the assistance) however I am now in the process of adding a thermal probe to the arduino and code to allow the system to register shifts in temperature then automatically adjust focus to match. My other option here is a pair of nichrome wire heaters wrapped around the entirety of the lens operated via a PID with a thermal probe to maintain the lens at a constant temperature all night thus negating thermal contraction.

3. Any missfocus causes flares on stars (I tested this to be sure it wasnt just the optics) the flare swaps sides of the star intra / extra focus. when its spot on, the stars are single pixel pinpoints.

4. Stellar profiles at f/4 are much smaller than at f/2.8, however the iris is not perfectly round. I am looking into having a sub-aperture mask 3D printed to bring the lens from f/2.8 to f/3.5 to tighten the stars without loosing too much speed.

5. My mount is great... I pushed quite a few 180sec test exposures with perfectly round stars with the setup, telling me that with guiding I should have absolutely no problem (in dark skies) going to 10~15 minute subs.. At only 3 minutes from home at f/2.8 the image is completely washed with light polution.

[Ryderscope]

Thanks for your NGC 253 shot Alex as it has given me a good idea for a target for my Canon F2.8 200mm prime lens. Its a nice composition with the Globular Cluster in the field.

I am also having issues with my lens adapter in that it is not a snug fit. I am attaching the 200mm lens to my QSI 683 CCD using the stock QSI adapter but it has rotational shift as well as it drops slightly under the weight of the lens. I have made up a very secure mounting plate but it is a bit of a guessing game as to exactly where to position the lens. It probably only has about .5mm (or less) of play but this is enough to throw off the image plane which is causing elongated stars in the corner of the image, not too dissimilar to what you are experiencing. I will be interested to see how you go making up a shim to suit your adapter. It may also be an issue with the distance between the lens and the focal plane of the CCD so a very thin shim may fix this. I will watch the results of your experiments with interest.

I don't see any much in the way of diffraction spikes which is interesting if you were capturing these without an aperture mask. For what it is worth, I purchased a step down adapter from ebay to use as an aperture mask and this works quite well on the 200mm lens. It steps down the front of the lens from 72mm to 49mm. Something to think about if this suits your requirements.

Thanks again for the idea on the NGC 253 image. My resulting FOV with the 200mm is about 5 degrees by 4 degrees so will suit this composition nicely.

Good luck with your set up Alex.
R

[glend]

Nice test shots Alex. With your modded camera there is much more Ha in that nebula, and the colour seems far too washed out. What processing was done?

[AlexN]

Rodney - as to the ngc253 image, I didn't even know that glob was there until I started the run..

I'm having a custom step down ring 3d printed as there are no commercially available 112-90mm step down rings produced.

Which one Glen? The m42 image I posted is the red channel only. The colour image was impossible to balance due to light pollution.

The balance in the images with the camera is decidedly red. I intend to get a clip in ha filter or a 36mm unmounted ha filter for the 300/2.8 drop in filter holder to combat the light pollution. It's funny with an 8" f/5 Newtonian the ight pollution seemed not all that bad but with a wide, fast aperture setup like the 300/2.8 the light and resulting gradients are painfully difficult to process out.

[strongmanmike]

Once you have sorted your issues Alex and get under some dark skies, you could have a pretty useful rig in your hands there, look forward to seeing what you can produce :thumbsup:

Mike

[RickS]

Very promising results, Alex.