Is my Super-Takumar 200 focused on infinity?

[dieg00]

Hi, I just recently bought a Super-Takumar 200mm f/4 to use with my unmodified Canon 60D and a basic tripod. Using the M42-EOS Neewer adapter, the lens appears to go to infinity focus but doesn't move past it. I'm scared of it not really reaching infinity focus, although appearing to do so.

Two days ago I tried to take a photo of M13 (a hard target for a first light, I know), and I obtained the following non-cropped image:

Cropping it and adjusting saturation and such I get:

Is it infinity focused? I also know I should expect some bloating at larger apertures, and this was done at f/5.6 using the mechanical blades (I have ordered but have yet to receive a few step down rings to prevent diffraction spikes).

In total I did 1500 lights (with a exposure of 0.8") at ISO 3200 and DeepSkyStacker stacked 1490 of them. I also did 100 bias, 100 darks and 100 flats (these ones where done pressing the camera against an iPad screen). This was done at a Bortle 6 location on the outskirts of Madrid, so I had to remove the light pollution with Photoshop.

I have read the focus can be adjusted but I'm afraid of opening the lens and having the solution be worse than the problem.

So, is it on focus? Are there any other tips or things you'd recommend me to do?

Thanks in advance!

Diego 

[Alien 13]

If the very faintest small stars are visible then its in focus, in fact in my view this is the only way to confirm and far better than the guess work when using a bat mask.

Alan

[alacant]

36 minutes ago, dieg00 said:

I'm afraid of opening the lens

Hi

No need to open the lens.

With the lens set conventional infinity against the physical stop, Unscrew each of three grub screws one turn each to loosen the focus grip. Next, rotate the grip only about 1/8 turn so that when tightened, it will propel the lens beyond infinity. Re-tighten by the same amount you loosened.

On the 200, the green and blue are in close agreement, leaving the red out of focus. Using live view at 10x on a moderately bright white star, rotate the grip until there is a pronounced red halo. Now twist the opposite way until the red halo just disappears. Focus masks will not get you this close.

You're close, but 5 minutes adjustment will allow you to make certain.

That's it. HTH.

Edited August 29, 2021 by alacant

[dieg00]

1 hour ago, Alien 13 said:

If the very faintest small stars are visible then its in focus, in fact in my view this is the only way to confirm and far better than the guess work when using a bat mask.

Alan

What faint stars would you recommend? On my pancake 24mm I would see if I can see the galilean moons through liveview as a check, for example. With the super-takumar it also happens, but it's a 200mm against a 24mm

[dieg00]

1 hour ago, alacant said:

Hi

No need to open the lens.

With the lens set conventional infinity against the physical stop, Unscrew each of three grub screws one turn each to loosen the focus grip. Next, rotate the grip only about 1/8 turn so that when tightened, it will propel the lens beyond infinity. Re-tighten by the same amount you loosened.

On the 200, the green and blue are in close agreement, leaving the red out of focus. Using live view at 10x on a moderately bright white star, rotate the grip until there is a pronounced red halo. Now twist the opposite way until the red halo just disappears. Focus masks will not get you this close.

You're close, but 5 minutes adjustment will allow you to make certain.

That's it. HTH.

Thanks for the info!

When you say the "grip only" what part are you referring to? The cylinder that you rotate to focus? 

Would doing this process alter the relation between the numbers on the focus rings and the real life situation? As in, would infinity still mean approximately infinity or would the infinity symbol still be the end of the focusing ring so it would mean more than infinity? I hope I make sense haha

Also, do I have to do the red halo process on f/4? 

[alacant]

8 minutes ago, dieg00 said:

would the infinity symbol still be the end of the focusing ring

My photo is with the adjustment made and with the focus up against the physical stop. 

11 minutes ago, dieg00 said:

red halo process on f/4? 

No.

 

[alacant]

11 minutes ago, dieg00 said:

The cylinder that you rotate to focus? 

Yes.

[dieg00]

1 hour ago, alacant said:

My photo is with the adjustment made and with the focus up against the physical stop. 

 

So when doing the adjustment I have to rotate it as if I was focusing on something closer to me? (Sorry if the question sounds stupid, I just want to be sure before I do anything).

Also, how could I revert the changes if I wanted?

[alacant]

10 hours ago, dieg00 said:

rotate it as if I was focusing on something closer to me

Yes.

[alacant]

11 hours ago, dieg00 said:

how could I revert the changes if I wanted?

Make a mark on the lens of the original orientation before you adjust.

But hey, they're around €50. Is it worth the hassle? If you want one for daytime use ¡cómprate otro!

Edited August 30, 2021 by alacant