Samyang (Opteka) 500mm F6.3 - Another low cost lens for AP
Being a fan of catadioprics, I was intrigued by this lens for some time..
When I saw the add on ebay, I decided to bite in.
The preliminary results are attached below.
Lens is decently sharp in the centre, a bit of coma in corners.
Not easy to focus, but this has to be done only once in a while anyway... I plan to add the ring which will fix the focus barrel..
Thx Bojan, I have been considering these for a while now but just wasn't sure. There is also a 600, and an 800 I think, that it would be good to see some tests from. Astro test, rather than land shots that is.
So it looks like it is quite capable for the price they ask.
Trev
It is interesting to see Bob Atkins website: http://www.bobatkins.com/photography..._500_f6-3.html
The focus he managed to obtain with this lens is unnbelievably bad.. I think he made a mistake (or he didn't have enough patience to focus properly, and this is not easy task due to backlash in the focussing mechanism. The focussing when lens is pointing to the horizon may be disturbed by changing the direction... to the zenith for example.. because the corrector lens can potentially slide back.
This problem can be sorted out like on those images: http://www.iceinspace.com.au/forum/a...e.php?a=142353 http://www.iceinspace.com.au/forum/a...e.php?a=143393
If the lens is used only for AP, this solution is not a problem, as the focussing must be done only once.. and then checked from time to time.
I focussed my Rubinar last year.. and the focus is still spot on.
I have just received this lens today. I'm hoping to get out and try it with some moonage tonight but currently the clouds are starting to roll in! Here is a shot of the school opposite my house with a range of about 400 meters. Not bad and I agree that the focus can be very precious. The focus was helped by the A7S having focus peaking where you can magnify the focus area up to 8X.
I'll try to get some astro shots up as soon as I can.
Nice. Magnified view is better for critical focusing rather than focus peaking. If you use focus peaking its better to have it set to low so the area highlighted as in focus is minimal. I find there is still a small adjustment to be made from magnified view over focus peaking.
The image is good but it looks like the focus is off a touch.
Thanks for the advice Greg. The difference in focus between in and out is a travel of 1-1.5mm. The action takes place completely within the borders of the infinity mark! The ring is fairly stiff and I could of taken a longer time fiddling to get it right but i was getting ready to go to work. I'm also thinking of making a Bhatinov mask and using this with the 8X zoom to get as close to focus as possible.
This spring arrangement (there is another one on the other side of the lens) removes focus backlash.
Because the focussing tread is quite steep, springs are intentionally not parallel with lens axis, to compensate for the tendency of the focus ring to rotate in the opposite direction due to spring tension.
Last week I bought one more specimen on ebay, for $75.. This one is branded Rokinon, DX variant.
First star tests indicated it is better than my older one (Opteka DG), it seems it doesn't have so prominent coma in frame corners..
So I decided it will pay off to improve the focusing mechanism, by adding stepper motor.
The control circuit was developed with Nico13 some 12~13 years ago, I built couple of them, and I am still using it :-)
I have both Rokinon and Samyang lenses, I believe they are one and the same, I may be wrong. I love my Samyang 14mm f2.8ED, the same lens Joe (OzEclipse) used to shoot his AMAZING aurora shots in Tasmania.
I have the Rokinon in 35mm f1.4 and 85mm f1.4 but I haven't tried the 2 Rokinon lenses for astro as of yet. If the weather ever clears up I may just get to trying them both but I don't think they are ED lenses.
I love the focusing mechanism and it's convinced me I have to get my mill on a stand I have yet to weld up, I really must get to it soon, brand new mill sitting in it's case for 3-4 years (health).
Yes, those lenses are the same (sort of.. they came from the same design department it seems) but not quite in terms of manufacturing..
I investigated this lens quite a lot and found out on Radojuva website that DG and DX are Chinese and Korean product (respectively).
Also, after checking Astrobin, it became obvious for me that there are good and really bad specimens.
That is why I decided to try this one.. and it seems it is better. I will take some longer exposures over next couple of nights and I 'll post the results here.
Also, after checking Astrobin, it became obvious for me that there are good and really bad specimens.
My first 14mm f2.8 could not achieve focus at infinity (manual focus unit) but it was swiftly returned and replaced with a high quality unit that can achieve focus. It's nowhere near where the infinity mark is and is a bit of fidgeting to get it right but once focused accurately it is sharp on the Milky Way in the right conditions.
I believe my 85mm I purchased used can not achieve infinity focus at f1.4 but should once I stop it down. I complained to the eBay seller and he p****d in my pocket about do this and that in live view but I neither had live view on my D80 nor access to a camera with it. I should have demanded a full refund, especially when the guy told me he had 2 of the same lens hence the sale, the first one was CRAP at f1.4 and I'm assuming that was the reason for 2 identical lenses in his gear.
I can find strip down information for the repair of the focal point on the 35 (which I believe to be sharp and have absolutely no idea how I even come to own it) and repair information for the 135 but not the 85mm and while I've always been prepared to just keep ripping things apart till I fix them or I destroy them (always the former, thankfully) I stopped at a certain point where I assumed going beyond there could make the lens completely useless.
In saying that there is NO doubt OzEclipse got a high quality lens in his kit, it can't just be the K1000.
DX is for APS-C sensor isn't it?
I have one DX Tamron zoom I use on my full frame Nikon but it's not the best (Vignetting). I got it cheap with a busted zoom mechanism but it didn't take long to figure that out and repair it (loose screw under the rubber the slot moved up and down on).
I have some images taken with Opteka 500mm DG, and the issue with coma is there, quite visible. I hope for the better with DX.. (no idea what DG or DX means.. )
On original package for Opteka, it says it is for full frame, but it is not even for APS.. I believe they didn't assemble it properly in the factory.. but we shall see :-)
Over weekend I did some testing again, and confirmed there is some astigmatism See attached image).. so I opened the lens today.. the main mirror retaining ring is glued to the frame and most likely over tightened..
I tried with acetone, but couldn't turn it (using the caliper as a tool..).
I think I will have to make a proper tool to do this job and/or apply more acetone to soften the glue enough so I can free the glass from the tube.
EDIT:
Success! more acetone definitely helped. Now, star test again.
How hard is it going to be getting the mirror adjustment spot on?
Trial and error I guess?
I have to figure out how to focus a 28mm wide angle lens (f2.8) without the aid of live view which is pathetic on my D810 in the dark (just noise shows) and the moon is the most unsuitable target for such a wide angle lens.
Strangely enough with my 14mm it was all trial and error, take shots, adjust the focus, write the shot number and adjustment down, come inside and put the card in my computer where I had a large screen I could actually see. It took a while but I now have a permanent mark where infinity is for proper focus.
The 28mm, I'm not too sure on but I'm using a PK to Nikon F adapter which could be causing the issues, it hasn't been a problem with any other Pentax lens (it's a Sicor with PK mount).
I'm going to try and get a dedicated Nikon 28mm. The problem is I want the 28mm f2.8 AI-S, an 81 onwards make and people want $500 plus for them. I have to remove the aperture wings (silver bracket) and set the non CPU lens data in my camera to use the thing anyway.
I don't care what anyone says, unless it was like some of their very rare lens builds it's not worth that money, not to me.
I may put a wanted thing in here and try my lock, someone could have one laying around they'd be willing to part with at a decent price.
Have you had any luck with the other lens with the un-removable screw?
How hard is it going to be getting the mirror adjustment spot on?
Trial and error I guess?..
If you are referring to colimation, there is none.. The mirror sits in its seat, not tightened, just touched.. so it is not deformed (hopefully)
And since this lens is going to be used for AP only, I am adjusting focus with Bahtinov mask on live screen. Focus is usually stable since the lens is small so it reaches thermal equilibrium relatively quickly.
For Solar Eclipse 2028, I am guessing I will adjust focus (with live view again) on some distant object on the horizon, before the event, when the temperature is already stable.
When I was adjusting focus on modified Canon 50mm F1.4 FD, I was also using live view, with the lens assembled but focus stops accessible for adjustment. so it was not entirely trial & error method :-)
Quote:
Originally Posted by Leo.G
Have you had any luck with the other lens with the un-removable screw?
Not yet.. I postponed the Astron Reflex for the day I am less nervous :-)
I will try with hot air gun (and small nozzle) and your method (I have cold spray.. and butane gas can be used as well).. but later , maybe this week.
Good luck with it Bojan.
You have Canon gear, it's much better to focus in the dark with live view than my Nikon D810 which is absolutely useless for live view. It's nothing but noise and I've oft read the same comment from other owners, it's a pity.
I have this probably stupid philosophy, if I can purchase a lens cheap enough to be prepared to throw it out if I ruin it I will (and have) strip it down to repair it whether electronics or mould on glass, front and/or rear elements. I won't touch middle elements, I'm not totally stupid.
I have picked up some very nice lenses quite cheap because of the faults and recovered them.
One was a zoom mechanism locking up, it was as simple as removing the rubber ring and screwing the screw the slot runs on back in except I removed the screw and put thread lock on so it won't happen again.
If I lose $50 I can wear that, not much more on a pension but despite what I may claim I'm far from a total idiot when it comes to disassembling absolutely anything and fixing the faults/reassembling the things, my son is the same..
