17 replies to this topic

[GlenM]

I was wondering if people used Bahtinov masks with their camera lenses. I would be grateful for any pointers about the use with camera lenses.

 

Thanks,

Glen.

 

 

[petert913]

I bought a small one for my telephoto lens.  The problem is the stars are not bright enough to really see

the spikes.  At least in my Canon LiveView.   Sirius and a few brightest ones, maybe.   Zooming in 10x

on the camera viewfinder does help. 

[RadOD]

Yes, I would never be without one.  When focusing, find the brightest star available to focus on, turn on live view, adjust aperature/ISO, zoom all the way in, and focus.  They are only a couple bucks but make life much easier.  

[GlenM]

Thanks for the quick reply,Peter. I thought this might be the case. Just wondering if it was worth £54 for a 72mm mask. It seemed a little pricey to me.

 

Clear Skies,

Glen.

[GlenM]

Yes, I would never be without one.  When focusing, find the brightest star available to focus on, turn on live view, adjust aperature/ISO, zoom all the way in, and focus.  They are only a couple bucks but make life much easier.  

A couple of bucks?

 

Glen.

[halx]

Thanks for the idea! (Something to 3D print for my 72x300 and play with ). However, for a typical fixed photo lens, I'd rather do a series of shots, then confirm the best one again, and semi-permanently fix the focusing ring at that position (a 3D printed set of rings for that may help as well). Tedious, but why the rush? You have to do that just once.

[einarin]

Just bought Bahtinov mask for 77mm (fits uv etc filter) and it was about $15.

[Jerry Lodriguss]

I never use them with my lenses.

 

Too much of a pain. You need a different one for different size lenses, and you have to remember to take them off.

 

And they are not any more accurate than using Live View at 10x because both methods just use your judgement to decided when the star is in focus.

 

Here are my tips for using Live View to focus:

 

http://www.astropix....w_focusing.html

 

Jerry

[MalVeauX]

I was wondering if people used Bahtinov masks with their camera lenses. I would be grateful for any pointers about the use with camera lenses.

 

Thanks,

Glen.

Heya,

 

I use one, with Live View too.

 

I got a little 58mm or so sized one. I simply put it in front of my lens, turn on Live View, adjust focus until I like the diffraction pattern, then take off the mask to inspect how it looks then lock it in. Done. Go on to shooting.

 

Very best,

[RadOD]

 

Yes, I would never be without one.  When focusing, find the brightest star available to focus on, turn on live view, adjust aperature/ISO, zoom all the way in, and focus.  They are only a couple bucks but make life much easier.  

A couple of bucks?

 

Glen.

 

Its only a piece of plastic with some slits cut in.

 

 

$12.95  https://smile.amazon.../dp/B01BLVKTVQ/

Edited by RadOD, 19 March 2017 - 03:32 PM.

[bmhjr]

What is the filter holder thing it says that needs?

[einarin]

"Snaps into a UV or Skylight filter"

[GlenM]

Thanks to everyone for the information.

 

Clear Skies,

Glen.

[halx]

Printed the mask for my 72/300:

 

 

Having an overcast, so used some distant lights for the first testing. The white one (below) is about 4 miles away, which is behind the hyperfocal range already. Red ones are 8 miles away (power grid pylons). I believe they are out of focus due to the chromatic aberration of the lens. As in the white one's "rays" I can see red spots also shifted to the left (which is as if the lens is focused to a closer distance, not to infinity). That's the "infinity" setting of the lens, which looks overshooting just a tiny bit.

 

 

By, the way, I had no problems seeing spikes through the optical viewfinder of the DSLR, using the 2x right angle attachment over the EP. That may not work with stars, indeed. I'll post more images and thoughts on the testing results in my blog here.

[Traveler]

"Snaps into a UV or Skylight filter"

 

How does one unscrew an UV filter from a camrea lens when done with the Bathinov mask, without changing the focus of the lens? 

Edited by Traveler, 21 March 2017 - 01:14 AM.

[einarin]

That might be a problem - therefore 'normal' Bahtinov masks might be better.

But last time I just put tape to lock the focus. And Bahtinov mask/filter was quite loosely screwed in place.

 

Alex, that looks like dense Bahtinov mask.

Interesting to see how it performs with real stars.

[halx]

einarin, you are right, I actually forgot to accustom for the PLA expansion drawing the slits and sticks simply equal in width. So the slits are a bit narrower than I wanted (they may look even narrower on the image as the mask is 1mm thick and imaged at an engle). But it works for me, as I don't trust my eyes anyway, always relying on the series of images analysis in the images editor to determine the best focus. The mask is still the great aid to that, as it's much more sensitive than just looking at the fuzzy star disk "transmutations" without it. Understanding the chromatic aberrations with it is also a significant step up, as for example for imaging Sun's prominences during an eclipse I now have the option to adjust the focus to make them sharper with that lens.

 

Also, this fixed focus 3 elements lens has a fantastic AP feature: the screw-on stop ring with 3 set screws on the front of the focusing barrel. It's defining the hard stop of the R&P focuser as it goes in. The lens is also all aluminum with very good machining. So, my plan is to focus on the lights in 10+ miles away (they are on the other side of my house building), which is way behind the hyperfocal distance of this lens for my camera's pixel pitch, and then adjust that ring to make the ideal infinity focus 100% repeatable without any guesswork (it's not there initially, as the lens has it's proprietary way of attaching to any camera brand's body.

[halx]

"Snaps into a UV or Skylight filter"

 
How does one unscrew an UV filter from a camrea lens when done with the Bathinov mask, without changing the focus of the lens?

My lens has the rack-and-pinion focuser, so that's not a problem. But there is another problem with the filter. It's shifting the focal plane:
 

 
That's two images of Sirus overlapped with subtraction algorithm. The effect is very small but it's there.

By the way. The Sirus (not perfectly focused yet).
 

 
And the same Sirus over the Treasure Island's lights row (6 miles away, taken right after the Sirus), to demonstrate that at the hyperfocal distance there is no difference in focusing.
 

 
(I think you've guessed it, but Sirius is second from the left).
 
And finally just for your enjoyment:



The row of four lights used for testing is at the bottom, slightly left off the center. Full size after the click. You can see how red lights are defocused due to the CA.

Edited by halx, 22 March 2017 - 12:18 PM.