Is this good enough

[shropshire lad]

Or do I need to get it spot on ..... 

Canon 80D 600mm f5.6 

 

Thanks 

[rl]

That is close but not quite perfect. It probably won't make much difference.

Why would you not get it spot on? Is it very difficult because the focus is coarse/ stiff?

[DaveS]

Yes, it's just a touch out, but I've found that "just a touch" can make the difference between nice sharp stars and a soft bloat.

[Elp]

Fine focus is very imperceptible at times, more so with camera lenses, it's like you have to rotate a touch but having done it you feel you haven't rotated at all but it's visible in the star shape.

[shropshire lad]

Thank you for the replies.

Yes it's quite difficult to fine tune the focus on my Sigma lens as just the slightest touch sends it way out.

 

paul

 

[moggi1964]

Sometimes good enough is exactly that.

There will be other occasions when it just drops into place and you get 'spot on'.

I found I wasted a lot of time over the years in a number of hobbles trying to get 'spot on' when good enough would have done the job.

That said, sometimes only 'spot on' will do.

I think I am beginning to spiral out of control 🤪😁

[alacant]

On 16/08/2023 at 15:12, shropshire lad said:

Sigma lens

So focusing with the mask will leave you with coloured halos around bright stars. Use it to get you close, then lose it.

Now, using zoomed in live view on the same star, adjust in tiny amounts until the blue [1] halo just disappears.

Cheers and HTH 

[1] not familiar with the 600 so the residual halo may be red; same idea.

Edited August 18, 2023 by alacant

[ollypenrice]

My (limited) experience with camera lenses says that you need a micro-focus to avoid going mad. Mechanical ones are available from Telescope Service. Alacant's point above makes sense, though.

Just putting an improvised lever on a lens or focuser can also help with micro-adjustment.

Olly

[shropshire lad]

2 hours ago, alacant said:

So focusing with the mask will leave you with coloured halos around bright stars. Use it to get you close, then lose it.

Now, using zoomed in live view on the same star, adjust in tiny amounts until the blue [1] halo just disappears.

Cheers and HTH 

[1] not familiar with the 600 so the residual halo may be red; same idea.

Sorry dont fully understand your answer, If I lose the mask then I will lose the coloured halo's wont I .... 

Also the Sigma lens is the 150-600mm f5-6.3 C lens.

[shropshire lad]

45 minutes ago, ollypenrice said:

My (limited) experience with camera lenses says that you need a micro-focus to avoid going mad. Mechanical ones are available from Telescope Service. Alacant's point above makes sense, though.

Just putting an improvised lever on a lens or focuser can also help with micro-adjustment.

Olly

How do you mean an improvised lever ?

 

[ollypenrice]

3 minutes ago, shropshire lad said:

How do you mean an improvised lever ?

 

Well, all you need is a lever attached to the focus ring, sticking out from it like a bicycle spoke, if you like. If the focus ring is the O the lever would stick out like this:  O----   The long lever lets you make smaller adustments.

Olly

Edited August 18, 2023 by ollypenrice
False click

[shropshire lad]

Sorry excuse my ignorance .... a lever on what and how.

 

[vlaiv]

2 minutes ago, shropshire lad said:

Sorry excuse my ignorance .... a lever on what and how.

 

Further you are from the axis of rotation - smaller angle for the same linear motion. So you can make fine adjustments with lever much more easily.

[ollypenrice]

3 minutes ago, shropshire lad said:

Sorry excuse my ignorance .... a lever on what and how.

 

Here's a link to a lever with push-pull micro asjusters. I had one. It's not bad.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3286_TS-Optics-Microfocuser-for-your-camera-lens-up-to-135-mm-Diameter.html

Olly

[ollypenrice]

2 minutes ago, vlaiv said:

Further you are from the axis of rotation - smaller angle for the same linear motion. So you can make fine adjustments with lever much more easily.

You even matched my red in your image, Vlad! Pure genius, as ever!!

lly

[shropshire lad]

My Lens

[andrew s]

1 minute ago, ollypenrice said:

Here's a link to a lever with push-pull micro asjusters. I had one. It's not bad.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3286_TS-Optics-Microfocuser-for-your-camera-lens-up-to-135-mm-Diameter.html

Olly

I have one you can have foc .PM me if your interested. Regards Andrew 

[vlaiv]

1 minute ago, ollypenrice said:

You even matched my red in your image, Vlad! Pure genius, as ever!!

And that was before I even saw that you edited your post

[shropshire lad]

Ak ok... I see now ... thanks for your replies and help on this.

[ollypenrice]

1 minute ago, vlaiv said:

And that was before I even saw that you edited your post

  It's not remarkable if you don't believe in the tensed theory of time (past, moving present, future.) And who could belive in a theory as naive as that one???

Olly

[vlaiv]

7 minutes ago, ollypenrice said:

  It's not remarkable if you don't believe in the tensed theory of time (past, moving present, future.) And who could belive in a theory as naive as that one???

Olly

And just like that (phrase that sounds familiar for some reason?) we jumped from focusing to this:

https://en.wikipedia.org/wiki/B-theory_of_time

 

[ollypenrice]

1 minute ago, vlaiv said:

And just like that (phrase that sounds familiar for some reason?) we jumped from focusing to this:

https://en.wikipedia.org/wiki/B-theory_of_time

 

Homework!  That's tomorrow taken care of, then. Oh no, wait,, I don't yet know if I'm a B-theorist or not so tomorrow may be an illusion...

lly

 

[Elp]

The lever is a very common thing in videography for focus pulling. From my use with all sorts of lenses both old and modern it's not really necessary though for star focussing, you can always reduce slight star bloat post process.

[shropshire lad]

8 hours ago, Elp said:

The lever is a very common thing in videography for focus pulling. From my use with all sorts of lenses both old and modern it's not really necessary though for star focussing, you can always reduce slight star bloat post process.

Thank you Elp, what software do you use for this?

Paul

 

[Elp]

PS or GIMP, many people apply a star reduction to their images to give more emphasis on the target.

When using a camera body I usually take a few images and zoom right in so you can judge the focus better. Some bodies also have focus assist where you can zoom in live and adjust focus, but I find you cant zoom is as much as zooming on the captured images.