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Posts posted by Uranium235

  1. The corners on the pacman are much improved. That leads me to think that the focus can be tweaked slightly to improve the overall field.

    One thing I used to do is use a ROI box on the offending corner (for quick loop), take an exposure, then tweak the focus very slightly.... "are the stars better or worse?", if not, go the other way... if yes - check the other corners to see if youve knocked anything out of focus - if its still good, youre ready to rock. Sometimes its bit of a compormise. It takes a bit of time to do, but its worth it.

    • Like 1

  2. On 12/09/2019 at 17:14, Adreneline said:

    Took this one of the Heart and Soul last night unguided on my new iOptron CEM25-EC.


    The image is 10x 120s + 180s + 300s multi-session combined in APP and post-processed in PI. I chose to use all the subs, even the one with the aircraft trail. There is minimal cropping to remove edge effects.

    I think the star shapes are pretty good for unguided. I think the odd shape stars in the corners are down to the lens but I'd be interested to hear what others think.

    Took thos one of NGC1499 after I'd finished the Ha of the Heart and Soul. This is also unguided, all 300s - 12 x Ha and OIII.


    The combination of CEM25 and 135mm+ASI1600 could make a great grab-n-go setup.


    Thanks for looking.


    The right hand side of your images displays out of focus stars. This also corresponds with the master flat you posted earlier.

    Whether that is due to droop in your imaging train, I dont know. But an idea would be to test the lens on a DSLR and take some flats with that - if you get the same vignetting pattern, it will be the lens. If not, then you need to look at the way its attached to your astro camera as to what is causing it.

  3. On 02/09/2019 at 21:07, JamesAstro2002 said:


    3 Hours of data on Andromeda with the 600D from last night.

    I noticed that I seem to have them oddly shaped stars again. Last time, I fixed this by undoing the primary mirror retention clips a bit as they were tight up against the mirror. Now that i've been able to get back out for a night of imaging, they're back again! Any ideas as to why this could be ? I double checked the clips again and they're still loose, although they are still touching the mirror, are they supposed to touch it or not? I also made sure that the primary collimation locking screws aren't overly tightened. Also, through my cheshire, collimation looks to be spot on.

    As for the mirror clips, there should be just enough room to slip a fag paper between the clip and the mirror... so get down the corner shop and grab a pack of rizla..lol  :D

    • Like 1
    • Haha 1

  4. On 29/08/2019 at 10:57, Adam J said:

    FOV looks too big for it to be the ASI178mm cool but I may be proved wrong when Rob replies. 

    Sorry, I've been a bit ill the past few days.

    The veil shot was with the qsi 683 ☺ overall I was pleased with the field flatness on that shot. It did quite well over a 22mm diagonal sensor. 

    I'll be firing up the 178 when I get my hands on the long overdue 135mm f2 lens. Been waiting over 2 weeks for it now... it's starting to take the Michael.

    • Like 1

  5. On 26/08/2019 at 20:11, matt_baker said:

    Last Tuesday, I managed to go out and image M13 just fine, with only a couple of stars in one corner being elongated due to my focuser tilt.

    Last night however, I was trying to image the Iris nebula and the stars looked awful.

    I made sure to collimate and make sure the focuser screws were tightened nicely. Although I did push the mirror up slightly with the collimation screws to try and minimize the drawtube obstruction.

    Collimation was done with a cheshire eyepiece and collimation cap.

    My focus was also good from my bhatinov mask.

    I think I know it's not caused by differential flexure, since the stars look awful even from a 5 second exposure which I've uploaded for all to see.

    Could anyone help me out?


    If you look closely at the corners, it will tell a story. The left side has normal coma (I assume youre using a corrector?), while the right  is a different type of distortion (radial).

    That would indicate some tilt, either in the focuser, the way the corrector sits in the drawtube, or whether you have any loose connections. You might need to take time to square your focuser, simply tightening up all the screws doesnt quite mean that its pointing at the right spot on the tube wall.  You have to remove the secondary and put in a marker for where the focuser tube should be pointing. There is stuff on youtube how how to do this, but I wouldnt attempt it until you have the bits required (digital calipers etc..)

    The stars in the middle are a bit so-so, but you didnt state whether you were guiding or not.

  6. 6 hours ago, Adam J said:

    whats your thoughts on reducing that to t2 thread straight after the M48 thread? would that result in vignetting?

    If the FW is attached directly to the camera - the m48-T2 adaptor will be about 11mm. 

    If you have a large format camera (diagonal of 22mm +l, I would use 36mm or 2 inch filters anyway. 

    The shorter I make the mod, the more options the user has got to configure it in a way that suits their camera. ☺

  7. 9 hours ago, Space Oddities said:

    Rob, I'm curious about the impact of your modification on the flange distance of the lens? Is it going to be similar to the Canon bayonet?

    I'm trying to keep it as close to the original distance of 44mm. But I can afford it to be up to 2-3 mm thicker (still leaves loads of room for a FW).

    I'm making the m48 thread just 4 or 5 mm.  That way any extension ring or FW will screw right up against the lens mod if you so wish ☺ 


    • Like 1

  8. 1 minute ago, KyleStoke said:

    Yeah didn't really mean it as a direct example more just a view of the inner workings, there isn't much in there. Seems to be as simple as 3 screws.

    I'm with you on the screw fits, I'm currently suffering from a horrible amount of tilt in my system  

    Its alright ;) Ive already seen the inner workings - a fellow SGL member was brave enough to take his apart so I could see if there are any nasty surprises lurking underneath the bayonet, and there isnt - so its all systems go :D

  9. 37 minutes ago, KyleStoke said:

    Hi Uranium, I am also very interested in these. 

    Take a look at this, I don't want to put the mockers on anything but seems very straightforward once you have a suitable replacement mount.



    This also opens up the possibility of getting any version of the lens and simply replacing the mount (unless I've missed something)

    Im aware that the same rule will apply to any variant of the 135mm (and maybe other lenses - even for mirrorless), the modification Im proposing is about getting completely away from bayonet connections and moving it to a screw-fit.

    Those links seem to deal with the idea of switching between lens mounts of various manufacturers, which doesnt really apply to what im doing as im ordering a custom mount (focused on AP) from scratch. Of course, once its modded you wont be able to just pop it on your DSLR again - unless you take 10min to swap out the lens mount :)

    Lets concentrate on the 135mm f2 MF for now, get it working - and then we can take a look at where else this can be applied.

  10. If the camera is modded (as in filters removed, but not replaced), the sensor may need to be re-shimmed to work properly with some lenses. I had to do it to avoid the hard infininity stop with the Samyang 135mm.

    Or, you can try using EOS utils to get a proper look at stars while focusing.

    Typically, a modded camera in my experience has a difference between what you see through the viewfinder, and what you see on the preview screen  - the preview screen is the one that tells the truth (for daytime photography anyway).

  11. 46 minutes ago, Adam J said:


    I will be going to Aus for a month early next year and am thinking of one of these for portable work with my ASI1600mm pro.

    I see a large number of people supporting both the lens and the camera as opposed to clamping only the lens or only the camera to the mount, is this strictly required or are people just doing it because droop / flex is an issue with the canon connector?


    Adam, Im currently working on a fix to completely eliminate the droop issue with the EOS bayonet connection (conversion of the lens to M48 thread). Its going to be a prototype so watch this space and I will have some news in a week or two.

    Currently, the lens needs to be supported because its quite heavy, which causes compression of the bayonet fitting as the mount slews about - its only secured with three springs, which isnt really strong enough when imagng at f2 tbh - which is why people are supporting the lens to minimise the movement. Moving to an all-threaded connection will (in theory) resolve that issue.

    Another bonus of going all threaded is that you will claw back the space taken up by the EOS-T2 adaptor.

    • Like 3
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