How to use Samsung 135mm F2 lens

[carastro]

As many of you know I am an experienced imager with a telescope, but not at all experienced with camera lens imaging.  My efforts so far have not been all that good, but some of it is down to a cheap lens and so I bought this lens on recommendation on here:

The trouble is I am a bit ignorant on how to use a camera lens.

I know about whether the aperture is wide or small F stop controls the speed, and I know about setting focus to infinity, but I am perplexed with the info on the side of the lens and all the instructions are in German.

I wonder if some kind soul could give this lens imaging newbie a brief and simple set of instructions.

Thanks

 

Carole 

 

Edited February 26, 2020 by carastro

[drjolo]

I think there are two things worth to mention about this lens.

One is aperture: it may happen that you will get little bit better image quality when you stop it down a little. But then bright stars will get spikes that comes from aperture blades. Some users (including me) attach "aperture stop ring" in the front of this lens to stop it a little and keep circular aperture shape.

Second one is mounting to camera. This connection needs to be stiff, because that is fast optics and do not forgive tilt or bending. And also backfocus distance needs to be kept, so you focus on the stars as close to infinity mark at the focusing ring as possible. This lens has internal focusing, so it is designed to have specific lens configuration at specific object distance. In my setup the ring is set about 5mm left to that mark when I focus at stars. And then I have pinpoint stars in the whole frame, but I have small chip - QHY163M. And SY135 is full frame lens. 

Then I think you should be very happy about this lens Here are my thoughts after (now) three years of having it https://astrojolo.com/gears/thirty-months-with-samyang-135-f-2/ 

Edited February 26, 2020 by drjolo

[carastro]

Thanks Lucas, but already you are using language I only have a small grasp of.  "Stopping down".  I know this is to do with the F stop, but is this going down in numbers.  ie, changing from F5 to F2 is this stopping down i.e. making the lens faster?

The infinity mark I believe is that figure of 8 on it's side.  

Where I have that thick vertical line is the furthest the lens will turn towards the 8.  So it is sitting on an L, could you clarify this please.

Thanks

Carole 

 

 

[carastro]

So as it is set in the picture, am I right in saying it is currently set at F2.8 and at infinity (focus needing checking of course).

Carole 

Edited February 26, 2020 by carastro

[PeterCPC]

I use one with my Canon DSLR and I find that the infinity mark (8)is spot on but be wary that it might not be. I use mine wide open and it's fine. Yours is set to 2.8.

Peter

[drjolo]

2 minutes ago, carastro said:

So as it is set in the picture, am I right in saying it is currently set at F2.8 and at infinity (focus needing checking of course).

Carole 

Yes, exactly - it is set to f/2.8 and almost at infinity (exact infinity would be when focus is set to vertical part of this L. 

"Fast" lens means less f number. f/2 is faster than f/4, because at f/2 you need less time to exposure the same scene. Stopping down means to set higher f number, so the actual aperture will be lower. 

[Frank the Troll]

5 minutes ago, carastro said:

Where I have that thick vertical line is the furthest the lens will turn towards the 8.  So it is sitting on an L, could you clarify this please.

Thanks

Carole 

 

 

The numbers 11. 16. 22. when matched with the F stop, will give you depth of field

You wont need to use them for astro

[carastro]

Quote

Stopping down means to set higher f number, so the actual aperture will be lower. 

Thanks that is the reverse to what I thought.  Silly term, to me down means lower duh!!

Carole 

[carastro]

Quote

I find that the infinity mark (8)is spot on

The focus doesn't go as far as the 8.  The furthest it goes it just past the L as in my photo, though I can see trying to find a position on a figure 8 could be difficult.   So infinity is on the upright of the L as some-one said above.  Focus on the lens goes a tiny way past that as in the photo. 

 

[carastro]

Thanks for your help guys, "think" I understand a bit better now.

Now I have to work out how to mount it.  I have read the Imaging with the Samyang thread and am now having a ponder.

Carole 

 

[Nova2000]

You need to step down your f ratio a bit . Like around 2.8 or 3.2 to get good round stars in the corners depending . I have not used ccd cameras but I know that you'll need some adapters to mount these lenses . And if I'm not wrong that 'L' you are referring to is the max point where you can spin your focuser .so basically that should be infinity. Hope this helps

Clear skies 

 

[happy-kat]

The middle graphics are indicating that when the lens is focused on what ever you are focused on for the aperture chosen (read the fan lines) it's showing the distance in front and behind that line in feet/metres what is in focus. So the smaller the aperture the wider the depth of field, so f22 (smaller aperture as the aperture blades have shrunk the aperture right down) gives the deepest depth of field. Portraits tend to use wide aperture like f4 to focus on face but the background is soft as out of focus, low number shallower the depth of field.

Edited February 26, 2020 by happy-kat
One should always proof read before submitting

[happy-kat]

The lens at f2 is tricky to focus I read, the infinity position is very fine as the distance either side is tight before falling off infinity.

[Craney]

This apparatus built by AstroKraken in France works well if you have a Focusing mask and Live-view on the camera /  or SharpCap etc with a CCD.

The central ring is finely adjusted  with two plastic knurled screws ( one of which is visible).    

here is the web-site. link.

http://www.astrokraken.fr/samyang-135mm-f-2-bracket-micro-focuser-a145773756

[carastro]

I have been looking at that bracket, your picture shows it much better than the one on the website and it looks good.  

Is the foot a Vixen shape, and is part of the kit supplied as he doesn't demonstrate fitting that bit.  

It definitely looks like a good option. 

Carole 

Edited February 26, 2020 by carastro

[carastro]

Quote

The middle graphics are indicating that when the lens is focused on what ever you are focused on for the aperture chosen (read the fan lines) it's showing the distance in front and behind that line in feet/metres what is in focus. So the smaller the aperture the wider the depth of field, so f22 (smaller aperture as the aperture blades have shrunk the aperture right down) gives the deepest depth of field. Portraits tend to use wide aperture like f4 to focus on face but the background is soft as out of focus, low number shallower the depth of field.

Thanks for your help, but I am afraid that went right over my head.  Don't suppose there is a simpler way of explaining it.

Carole 

[Gina]

Depth of field only really applies to terrestrial photography though a stopped down lens (smaller aperture) will be less critical of focus.  Trouble is, the more you stop down the less light gets through and you need longer exposures.  Focussing for lenses is extremely critical and I have spent years trying to get this right.  Having a 3D printer to create special parts helps enormously.

[happy-kat]

Thought might as well expand

A is the line that is your focus, currently showing for your lens infinity

B is if say you focused on instead a near by tree the focus line would have moved into the feet/metre scale, the distance to what you focused on

C is read with A , take the aperture being used C and refer to A for the depth of field spread for the  aperture at the selected focus B.

I see this more on old manual lenses, none of my new lenses have it even those with mechanical focus. My old lenses have the full range of apertures on the lens.

Edited February 27, 2020 by happy-kat
tried to make it clearer to read as I was ambiguous which was misleading

[kirkster501]

Here is my wide-field Samyang 135mm setup.

Edited February 26, 2020 by kirkster501

[Craney]

20 hours ago, Craney said:

 

 

19 hours ago, carastro said:

I have been looking at that bracket, your picture shows it much better than the one on the website and it looks good.  

Is the foot a Vixen shape, and is part of the kit supplied as he doesn't demonstrate fitting that bit.  

 

Hi Carole, I got the picture from the website   (  ) . ..... my photo must be on another page from the one you looked at....  Although I have bought a second hand version of this kit and it is residing on my mount as I speak.    I will take a picture of it tonight and post it on this thread like others have for useful information.

To answer your question,  yes it is a Vixen styled dovetail but it is made out of black plastic.   All the kit above is made on a 3D printer by the looks of it.    I think the hole spacings for the rings on the dovetail will be critical drilled for the 135mm so that the lens is evenly balanced and you can have access to the focusing ring itself.    The central ring in the picture  pushes/pulls from that top rail to give fine adjust on the focus whilst actually holding onto the focus ring of the lens.   The outer rings ( furthest left /right)  just grip the lens and secure it to the lower dovetail.

The guy I bought my gear from had collected all the relevant bits from Astro-Kraken, and so I had really a working unit from the get-go.    He included an AstroDad electronic focuser unit as well, but as yet my brain is just getting used to the plastic screw adjuster.... that is a future project.

Hope this helps.

Sean.

Edited February 27, 2020 by Craney

[fireballxl5]

17 hours ago, happy-kat said:

Thought might as well expand

A is the line that is your focus, currently showing for your lens infinity

B is if say you focused on instead a near by tree outside the focus line would have moved into the feet/metre scale, the distance to what you focused on

C is showing the depth of field spread for the various apertures.

I see this more on old manual lenses, none of my new lenses have it even those with mechanical focus. My old lenses have the full range of apertures on the lens.

Shirely C is the aperture setting, which does determine depth of field at a given focus distance.

 

[Gina]

1. B is the focus sleeve.
2. A is the depth of field.
3. C is the aperture ring.

[happy-kat]

I have updated my reply as I realised reading the comment above I had not added enough text to put in words what my head was thinking :-)

[sploo]

Late to the day, but I am a camera/photography lens guy who's trying to understand telescopes, so... for this lens:

Stopping down is reducing the physical size of the aperture (which means going to a larger f-stop number). The f-stop is the ratio of the focal length to the physical aperture size. E.g. 135mm focal length at f/2 is 135/2=67.5mm aperture. Stopping down to f/4 would result in the lens having a 135/4=33.75mm aperture.

At (or near) infinity focus, the depth of field should be pretty large, so it shouldn't be too hard to focus on stars even at f/2 (anything from a few hundred meters away should be in focus).

Good camera lenses generally get a bit better when stopped down a little from their maximum aperture (e.g. maybe f/2.8 for this lens). Having said that, the extra light collection of f/2 may be more valuable to you than the extra sharpness (depending on your preferences). Wide open you'll also likely get some vignetting (darkening of the corners).

The area of the aperture is inversely proportional to the square of the square of the f-stop; in simple terms, if the f-stop is 1.41x smaller (the square root of 2) then you get twice the light collection. I.e. f/2 has twice the light collecting area of f/2.8. Each time you stop down by ~1.41x, (f/2->f/2.8->f/4->f/5.6->f/8) your required exposure time will double.

Manual focus lenses usually had a hard stop at infinity, but autofocus lenses usually focus a bit past infinity (to allow the focus motor to overshoot without causing damage). That said, some modern manual focus lenses may also focus just beyond infinity too. I find that electrical insulation tape is great for preventing the focus ring from being accidentally bumped once set.

The depth of field scale is indicating what near and far distances should (just) still be in focus at f/11, f/16 and f/22; but at infinity focus I wouldn't worry too much. It's only when focusing closer that you'll really see the shallow depth of field from a large aperture (small f-stop number) come into play.

If you're putting the lens in front of a crop sensor camera (one that's smaller than the "full frame" 36x24mm) then you'll only see a smaller image circle projected by the lens. In my (still limited) understanding of eyepieces, this would be like having the same focal length eyepiece, but with a smaller field of view. Photographers often talk about the "reach" of smaller sensors, because ultimately if you're displaying the resulting image at the same print size it appears that the smaller sensor has "zoomed" in further (but it's only because you're taking a crop from the middle of the lens projection, and printing it at the same size). In simple terms, a Canon crop sensor DSLR (i.e. anything that isn't a 5D or 1D) has a 1.6x smaller sensor than full frame, and will give a you field of view similar to a 135x1.6=216mm camera lens on a full frame camera.

Edited February 28, 2020 by sploo

[Gina]

One thing to consider with lenses intended for terrestrial photography is that they are not fully apochromatic (APO) into the deep red where Ha and SII wavelengths lie.  This means that you need to change focus when changing filters.  For RGB you may notice a change in focus for the Red whilst the Luminance image looks rather soft.

Edited February 28, 2020 by Gina