A Slice of Cassiopeia

[Knight of Clear Skies]

Another outing for the 135mm Super-Takumar.   The main goal of this run was to try and polar align more carefully and see if I could get longer subs out of my mount - if I get myself an LP filter I suspect I'll need longer exposures to get the best out of it. Ideally I'd like to be able to get 3 or 4 minutes at 250mm.

The bright star right of centre is Schedar with the Pacman Nebula below. 10(or 11?)x180 second subs at ISO 800, 20 dark bias, no darks or flats,135mm lens at f4.5. There is a little vignetting, so I'm going to have another go at taking flats.

Looking at the individual subs the best three or four show no obvious trailing while the rest are trailing a little. Then the 11th sub has very bad trailing (I suspect I forgot to uncheck this sub before stacking, but it doesn't seem to have done much harm to the final image, which I'm happy with). I'd appreciate a little help diagnosing the problem please.

Here's a screen grab of DSS, showing the scores for the individual subs:

There are a few things to notice here. The sky background steadily drops as the target climbs in altitude. It also drops quickly between IMG_1946 and IMG_1948 - this was around midnight when much of the local street lighting gets turned off. I can see the best FWHM value and star count was obtained with the penultimate sub - this is good as it shows that heat build up in the camera isn't a problem. I give the camera 15 seconds between subs which seems to be fine. Looking at the subs the lower scores are correlated with visible trailing, so tracking is causing the drop in sub quality rather than changes in seeing conditions or anything else. The close up at the top left shows how bad the final sub is.

I think my polar alignment was good enough for 135mm, as I did get some clean subs. It appears that the mount is tracking unevenly, I can think of a couple possible causes. The mount isn't properly balanced, the camera and lens being quite a bit heavier than the balance bar. I may have to ring something up as I suspect the counterweights I have may be too heavy. When I sort this out, should I run with the camera or counter-weight end a touch heavy, to encourage the gears to engage?

The other suspect is the batteries which may be towards the end of their life. I have no idea how long they will last but they have put in many hours of work so far. When they expire I'll switch to a set of rechargeables, and make sure they have plenty of charge before taking the mount out.

Does this all sound sensible, and does anyone have any other suggestions please?

[jambouk]

Lovely image. I love this widefield stuff.

James

[happy-kat]

Do like these images.

[Leveye]

Looks great. I love using my 60's Takumars for astrowork. Try gradient xterminator for your gradient issues. Works great I find. You want to go slightly east heavy to ensure the gears are pulling and not pushing so camera side yes.

[Alien 13]

Another good image i think you have answered most of your questions yourself but these are my thoughts.

Batteries need to be in a good state the RA motor draws 290mA when tracking 390mA on a slew (figures i measured on my mount) i never tried rechargables with mine because they are only 1.2V which x 4 gives 4.8V, i either use std alkaline or a 12v power pack running into a DC-DC convertor set at 6,1V.

Balance is important and i use the heavy weight as close to the pivot point as possible making it very slightly counterweight heavy (you have to unlock the RA setting circle and remove the screw to get it to swing freely)

Play in the camera and lens mounting needs to be removed most of the EOS adapters i have tried are a little loose.

I dont know what type of remote you are using but make sure the cable is not inducing any drag etc.

Polar alignment is easier if you use a camera RA viewfinder on the polarscope it doesnt need to be attached just held in place is fine this allows the mount to be used at its min height without introducing contorsions.

Hope this helps

Alan

[jambouk]

A smear of blue tak under the eos-t2 ring against the camera body reduces the play there.

[Owmuchonomy]

A great demonstration of the depth and richness of the true star field. Just as an aside I find that I can predict bad subs. I picked up that this is not unusual and corresponds to a cyclical issue with my (all?) mount(s). So for example if your mount and motors have such an idiosyncracy you might find every 11th or 12th sub was poor based on the exposure parameters above. Now I know about it, it doesn't bother me at all.

[badger111]

That looks absolutely amazing

[Knight of Clear Skies]

Thanks for the comments everyone.

Looks great. I love using my 60's Takumars for astrowork. Try gradient xterminator for your gradient issues. Works great I find. You want to go slightly east heavy to ensure the gears are pulling and not pushing so camera side yes.

Another good image i think you have answered most of your questions yourself but these are my thoughts.

Batteries need to be in a good state the RA motor draws 290mA when tracking 390mA on a slew (figures i measured on my mount) i never tried rechargables with mine because they are only 1.2V which x 4 gives 4.8V, i either use std alkaline or a 12v power pack running into a DC-DC convertor set at 6,1V.

Balance is important and i use the heavy weight as close to the pivot point as possible making it very slightly counterweight heavy (you have to unlock the RA setting circle and remove the screw to get it to swing freely)

Play in the camera and lens mounting needs to be removed most of the EOS adapters i have tried are a little loose.

I dont know what type of remote you are using but make sure the cable is not inducing any drag etc.

Polar alignment is easier if you use a camera RA viewfinder on the polarscope it doesnt need to be attached just held in place is fine this allows the mount to be used at its min height without introducing contorsions.

Hope this helps

Alan

All helpful thanks. Only one problem - you say go counterweight heavy while Leveye says camera heavy, so I'm not sure which I should do.

A great demonstration of the depth and richness of the true star field. Just as an aside I find that I can predict bad subs. I picked up that this is not unusual and corresponds to a cyclical issue with my (all?) mount(s). So for example if your mount and motors have such an idiosyncracy you might find every 11th or 12th sub was poor based on the exposure parameters above. Now I know about it, it doesn't bother me at all.

I'll bear that in mind thanks. If I can run a few sessions with good polar alignment I might be able to spot any systematic errors from the sub offsets in DSS. Hopefully the mount can do better if I sort out the balance. I know the EQ3-2 isn't really designed for precise tracking, but using short focal lengths should hide a lot of the periodic errors.

[Alien 13]

All helpful thanks. Only one problem - you say go counterweight heavy while Leveye says camera heavy, so I'm not sure which I should do.

Try both it depends on any errors on the worm i think Leveye`s method is the norm.

Alan

[VigdisVZ]

Great image. The richness is stunning.

My only two minor issues would be it's a tad sharp, and I would like to see some more color brought out.

Keep it up!

[Pete Presland]

the direction is the important thing in off setting the balance slightly, as Leveye says East heavy is the tried and tested method.

[Knight of Clear Skies]

Great image. The richness is stunning.

My only two minor issues would be it's a tad sharp, and I would like to see some more color brought out.

Keep it up!

Thanks for the feedback. I agree more colour would be nice but I'm struggling against LP in Hertfordshire, when I try boosting the saturation it starts looking ugly. I had to magic select the Pacman and boost that up separately. I'll try bringing the sharpness down and see what it looks like.

the direction is the important thing in off setting the balance slightly, as Leveye says East heavy is the tried and tested method.

I'm still confused I'm afraid, so I should run counterweight or camera heavy depending on which part of the mount is pointing East?

[glowingturnip]

I'm still confused I'm afraid, so I should run counterweight or camera heavy depending on which part of the mount is pointing East?

move the weights to the East, seems to be the rule. Just a smidge though

[Knight of Clear Skies]

Got it thanks.

[wxsatuser]

All helpful thanks. Only one problem - you say go counterweight heavy while Leveye says camera heavy, so I'm not sure which I should do.

Try both it depends on any errors on the worm i think Leveye`s method is the norm.

Alan

Nice image with that setup.

I was under the impression that east of the meridian was weights slightly heavy and west of the meridian camera heavy.

May be what I have read is not right.

confused of Sussex

[dph1nm]

Hey, aren't those pixel shifts rather huge? If this is a 135mm lens on a Canon1100D then I reckon you have about 8" pixels - so you have moved about 90" in X and 160" in Y from beginning to end. That does seem quite a lot.

NigelM