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Posts posted by Uranium235

  1. 37 minutes ago, Icesheet said:

    Looks like a nice sharp and flat image. Did you stop the lens down here? Looks like some diffraction spikes on the brighter stars?


    Edit: I see it has 10 blades so you would expect to see more spikes I suppose? Is it something else?

    This was taken with the lens wide open. When you have exact focus you will always get diffraction spikes - they are caused by the clips that hold the lens elements in place (its a very common occurance).

    The adjustments required however to get to this stage are very...very... fine.  On a centrally focused star there was a little corner distortion (though equal and distribited evenly) - but if you move the star 2/3rds of the way out to the corner, then refocus it flattened the field out.

    Not really half the story really though. Ive only gotten to this stage because I swapped out my adaptors twice, then had to install a 50 micron (0.05mm) shim on the camera becuase it had a bit of tilt. Still more adjustments to make though, I had the spacing set to 56.5mm - but I think at least 0.5mm can come off that.

    • Thanks 1

  2. Looks like it might be on for tonight. But its going to be a short tun, by the time I get home I would have been working for 14 hours, no way have I got the legs for a late nighter..lol 

    A couple of hours in Ha should be enough for a quick look to see if everything is as it should be.

    I'll just point it at Sadr and fire away with reckless abandon...lol... should get something interesting, :D

    • Like 1

  3. 4 hours ago, ollypenrice said:

    Could we have a recording of the lens cap going 'Ding' please?


    Next time I take it out, I'll give the dew shield a ding for ya :D  It back under wraps for the next few days atm, its looking like at tleast Thur or Fri next week before it clears up.  The actual lens cap is the only plastic part on it  :)   which probably accounts for its weight. 

    • Like 1

  4. 29 minutes ago, Alien 13 said:

    Nice unboxing but do think you need to beg/borrow/steal a Canon 6D or similar as this will likely be its favored partner..


    Unfortunately, I dont know anybody local with such a camera (35mm). And its going to be pretty much "grab and go" short notice sessions.

    If it satisfies the KAF8300 and APS-C to the point where you really cant tell the difference between the two (in terms of flatness) - theres a high chance it will be good with something larger... but thats just speculation at the moment. Lets just get it up and running, and see whats what.



    Dont forget, there have been many claims in the past where the manufacturer states that its good up to 35mm. (or beyond).. but thats rarely been the case. The KAF8300 has a 22mm diagonal, that is the minimum requirement for me. As mentioned in my video, if you cant get those corners youre just wasting data/pixels/time - not so bad if youre just doing one frame (and crop).... but I want to build mosaics.

    • Like 1

  5. 9 hours ago, david_taurus83 said:

    I had ordered a RedCat this week as my Canon 135 is no good at F2 and I can't get a clip in LP filter for my 6D. Have I made the right choice? Hmmm🤔

    We wont know until these thunderstorms/cloud go away :)

    This sits nicely between a 135mm and a Redcat.... and if it works as it should, it could beat both of them in terms of field flatness.  I still cant get over how heavy it is, very very solid in construction...lol.. quite like the way the dewshield goes "ding" when you flick it :D

  6. The 80ED is about as simple as it gets.

    Buy the 0.85x FF/FR, screw it to the drawtube (rock solid). Its spacing should be 55mm to the sensor. Use the M48 to T-Ring adaptor, that is always 11mm (for Canon), then the other 44mm is made by the backfocus of your camera = 55mm automatically achieved. 

    If at first you find the focuser a bit lacking in grip, you need to pinch up the tension - I find you have to do that to all stock skywatcher (crayford) focusers. As soon as its able to hold the camera against gravity, you should leave it there (dont do it up too tight).

    • Thanks 1

  7. Well, searching for a place to do this has uncovered some smashing imaging spots just over the border in Shropshire - just 15min drive from my house.

    The 130pds would have been completely unsuitable for this so I opted for the little 50mm Canon. But, being as the image run started before midnight, the Sun still had quite an influence on the images (baaad gradient), so I cropped that bit out and did my best to eliminate what was left. Seem to have gotten both tails now :)

    I did set up the guider, but didnt actually use it - I found it easier just for locating the comet (using the guide cam).


    40x30s Canon 1000d / Canon 50mm @f3.2




    • Like 6

  8. 3 hours ago, michael8554 said:

    6) performance wide open and stopped down


    Oh, I'll be looking to run it wide open all the time ;)  whats the point in imaging at a speed slower than its maximum? If youre paying for an f4 flatfield, you expect it to be flat at f4 - no messing about required (thats what people want to know).

    I remember getting the f2 Samyang because it was flat at f2, not because I wanted to slow it down :) 

    Though it might be worth taking it up a couple of stops, cant see there being that much difference if its already flat over APS-C (at f4)... perhaps slightly tighter stars but thats about it.

  9. On 13/07/2020 at 19:31, Adreneline said:

    I'm coming to the conclusion that the Samyang 135mm + ASI1600 might not be the best combination to capture the Squid nebula within the Bat Nebula (Sh2-129). This is 60 mins of Ha and SII and 180 mins of OIII (all 180s subs).

    I'll go for more OIII but I'm not confident I have the resolving power! There again my processing skills may be the limiting factor.

    Thanks for looking.



    Going for the squid with ANY telescope/lens/camera is a recipie for insantiy... youve done well to get some of it. Ive known people spending 40+ hours, just to get that little bit.

    • Like 1

  10. 16 hours ago, Alien 13 said:

    I am not entirely convinced by this lens, not enough elements for my liking but would like to see a head to head with the Canon 200mm f/2.8 set to f/4 or even the "cheap" 70-200mm f/4 L lens used wide open.


    There are a few tests I can do to see how it gets on.

    1) Corners (first and foremost)

    2) B-mask test (focus on green, then switch between red and blue to see how much movement there is in the diffraction pattern)

    3) OSC (use a DSLR to take an image - then split the channels and inspect star size/focus)

    4) Reaction to drops in ambient temperature - would be interesting as this lens weighs a whopping 1.8kg

    5) Mosaic building capability (it has to be very flat for you to effectively build a mosaic without wasting valuable data)

    • Like 2
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