Can you use a Bahtinov Mask on a camera lens?

[Star Struck]

I hope this is not a stupid question (guess I will find out shortly...).

Can you use a Bahtinov mask on a normal wide angle camera lens?

I have tried taking a few star trail photos using a DSLR and a normal wide angle camera lens but have had an awful job in getting the focus right.

Infinity seems to move and is not actually on the infinity marker on the focus scale. It has been a real pain so I am looking for some help here.

 

Tony

 

[Davey-T]

Never tried it, you should be able to focus zoomed in on live view, a dob of blue tack on the edge of the focus ring is good as the focus can move after you've set it, also need to do the same on the zoom ring if it's a zoom lens.

Dave

[Guest]

Hi Tony,

Actually, there are not STUPID QUESTIONS, only the answers could be STUPID..

I have an CANON EF 300 Lens + EOS600D-a, and I did cut out my own BAHTINOV MASK, by using the BAHTINOV MASK GENERATOR, but since I have APT I did stop using the BAHTONIV MASK, due to APT can also FOCUS automatically the CANON EF300 AF Lens on the SPOT..

Cheers

 

Martin

 

 

[Helen]

Not a stupid question at all.  The answer appears to be yes  Here's a commercial one http://www.lonelyspeck.com/sharpstar/ but given the principle clearly works then a normal bahtinov would seem ok too.  Alternatively I've been tempted to try a Y mask...  As I've just started actually doing widefield, rather than just thinking about it, I need to sort something out now!  

Helen

[frugal]

Somewhere in my box of bits I actually have a bahtinov mask specifically for camera lenses. Of course I no longer have any idea where I got it from. I never used it for wide angle, only zoomed in (135-300mm). There is no reason why it should not work, just make sure you pick a bright star to concentrate on, use a fairly long exposure and high ISO, and zoom right in on the photo to check the spikes as they will be quite small.

[iapa]

1 hour ago, Star Struck said:

I hope this is not a stupid question (guess I will find out shortly...).

Can you use a Bahtinov mask on a normal wide angle camera lens?

I have tried taking a few star trail photos using a DSLR and a normal wide angle camera lens but have had an awful job in getting the focus right.

Infinity seems to move and is not actually on the infinity marker on the focus scale. It has been a real pain so I am looking for some help here.

 

Tony

 

I have two different diameter ones purchased die a Nikon 300mm, the other was a canon 'nifty fifty' if I recall correctly.

Depends what you mean by 'standard' wide angle.

the wider the angle to' he more the glass will protrude beyond the end of the lens body - in those circumstances I'd not try in case of scratching the glass

Having said that, I imagine that if the lens is threaded for filters I've text it to be OK

f2 28mm lens I doubt it would fit.

My masks came from Gerd Neumann in Germany

 

 

[Alien 13]

I have my doubts about Bat masks on camera lenses in general but especially wide ones, the mask might give you a nice focus point in the center of the screen but is that what you want? I prefer thirds focusing away from the center using live view x 10 on a dim star, for me it gets a better overall focus.

Alan

[Star Struck]

Many thanks to all who replied.

I might try and follow the Y mask route first cos it is so cheap and easy to make.

Failing that I will investigate the SharpStar product as that fits nicely with the Lee filter system that I have.

 

Tony

[Helen]

17 hours ago, Alien 13 said:

I have my doubts about Bat masks on camera lenses in general but especially wide ones, the mask might give you a nice focus point in the center of the screen but is that what you want? I prefer thirds focusing away from the center using live view x 10 on a dim star, for me it gets a better overall focus.

Alan

 

As a novice, that is really useful info for me - thanks!  Could you put a brightish star a third out just for focusing with a b-mask and then re-compose?

Helen

[adder001]

Hi There,

I use one all the time it makes focusing so much easier although I've never tried it on a wide angle lens. I use it on my 300mm zoom. I originally bought it for my 90mm diameter telescope, I think it was about £12.

It has 3 adjustable screw lugs which you effectively clamp to the outside of the tube.

With my camera lens I use a lens hood which brings the diameter to about 70mm and just rest it on the front of the hood using the lugs.

I take a 20sec exposure at 1600ISO of a bright star and then check the picture afterwards. You will get the classic pattern, then if adjustment necessary move the focus to the left and check the pattern. If it improves keeps going in that direction until correct, if worse go the other way. The whole process takes a few minutes but you get perfect focus.

Here are some examples. The pattern doesn't show that well as a jpg but on the camera lcd it really shows up and also pictures of how it is attached

 

[Alien 13]

53 minutes ago, Helen said:

 

As a novice, that is really useful info for me - thanks!  Could you put a brightish star a third out just for focusing with a b-mask and then re-compose?

Helen

I am sure its worth a try, it might be more awkward though if you have to take a short exposure rather than it being visible with live view.

Alan

[carastro]

I have the same problem, and in the end resorted to a Y mask.  It is great to have extra aids such as APT, but I am planning to take it abroad on holiday and won't be able to take loads of equipment with me I think the Manfrotto tripod, the Skytracker and the DSLR will be my limit with carry on luggage etc, so will have to do it manually.  

Finding a way to hang the Y mask on the lens and at the same time focus it was not easy either the last time I tried, but take an exposure for about 15 secs sounds a good idea.  

Must practice before I go.

Carole 

 

[iapa]

Found the ones I used

58mm thread on for the Canon 300mm lens, and 67mm for the Nikon 300mm

I threaded them on until they just caught, focused, then taped the focus control to keep focus 'locked' then carefully remove the mask.

Before I used the masks, after I though i was focused I taped it anyway as I found the focus would shift due to gravity pulling the glass.

 

 

[Stub Mandrel]

Yes.

[iapa]

2 minutes ago, Stub Mandrel said:

Yes.

I remember a video (AstronomyShed's I think) where there was a warning about temperature related shrinkage with some of the the material used to make these masks.

This looks like a perfect example

[Stub Mandrel]

2 hours ago, iapa said:

I remember a video (AstronomyShed's I think) where there was a warning about temperature related shrinkage with some of the the material used to make these masks.

As long as the bars are pretty much straight and it fits over the lens, exact size is immaterial.

[iapa]

1 hour ago, Stub Mandrel said:

As long as the bars are pretty much straight and it fits over the lens, exact size is immaterial.

I thought I read somewhere that masks are actually cut specific to focal length? 

Need to look into that one.

 

Found it

https://www.cloudynights.com/topic/178843-revolutionary-new-way-of-focusing-no-less/

the slots are cut to focal length.

[Stub Mandrel]

19 minutes ago, iapa said:

I thought I read somewhere that masks are actually cut specific to focal length? 

Need to look into that one.

 

Found it

https://www.cloudynights.com/topic/178843-revolutionary-new-way-of-focusing-no-less/

the slots are cut to focal length.

In theory, however what is the 'optimum' size of the image on the sensor? It could be twice as big or half as big and still be perfectly usable, just bigger is easier to see but dimmer and vice versa. The fact is that a simple twig with a 'Y' shape demonstrates that what really matters is just the edges, even the angles aren't critical.

[iapa]

1 minute ago, Stub Mandrel said:

In theory, however what is the 'optimum' size of the image on the sensor? It could be twice as big or half as big and still be perfectly usable, just bigger is easier to see but dimmer and vice versa. The fact is that a simple twig with a 'Y' shape demonstrates that what really matters is just the edges, even the angles aren't critical.

Good question. Big enough to see clearly?

So, once again, it is personal preference/requirement/perception for this game.

 

[Stub Mandrel]

29 minutes ago, iapa said:

Good question. Big enough to see clearly?

So, once again, it is personal preference/requirement/perception for this game.

And the resolution of your sensor!