Manual focus lens

[dannat]

Question: to focus a manual focus lens would i still make a small hartman mask, or is there another way?

[Radar]

G'day Dannat,

A hartman mask is one way, and it's quite reliable. Another way is to use a cheap webcam or ccd camera. It depends on exactly what you are focusing though. Are you focusing a camera through a telescope? Or just a camera lens through a camera body?

If you are just using a camera lens and you are shooting widefield images, then simply set your focus to infinity.

What equipment are you using?

Ray

[dannat]

yes am just using a camera lens attached to camera, the infinity point of the focus I can see is not quite right

[Radar]

Is this a film camera? What make and size is the lens? Have you taken any photo's of stars through it yet, and if so, can you post the results? A lot can be learnt by looking at a photo.

When you say that the infinity setting is not quite right, do you mean your results still seem blurry when you are using that setting? Or something else?

Cheers

Ray

[dannat]

oops not a film camera, but is a zuiko 200mm prime. the focus is slightly out at infinity, needs to be tweaked back a fraction

[Dragon Man]

oops not a film camera, but is a zuiko 200mm prime. the focus is slightly out at infinity, needs to be tweaked back a fractionSo does both the lenses on my canon 350d. Infinity is NOT focus on either of them, but slightly back from infinity is :thumbsupmate:

[Radar]

Dannat the way I would focus a camera and lens configuration like this is to do a step by step process with notepad and pen.

I would point the camera (on a tripod or piggybacking a scope)at a bright star.

I would get the lens to a point of close focus then take a picture. Write down the exact position of where the focus adjuster was for the first picture. Move the focus adjuster along a bit, then take another photo, write down that position, and continue like that until you are sure you've covered the point of good focus. Then when you examine all your photo's from this focusing test, you'll know exactly where your best focus is on that lens.

I know that's not the quickest and handiest way to do it, but for a lens like that, its probably the most reliable. Whenever you are using that configuration of camera and lens you'll always know exactly where to turn that focuser to. You won't even have to look through the lens.

You could even do this test at different F-stops.

With things like hartman masks you still need to look through the lens, and this can be difficult if the camera is on a wierd angle or the object is dim.

If I was in your shoes, I would do the note pad and pen technique to ensure I knew the lens inside and out.

I hope this helps. Please post some results if you go ahead and do this.

Ray

[Erwin]

on my 70-200 2,8 IS, and 17-40 from canon, infinity works perfect.
on 200 2,8 prime also, and 10-17 from tokina.

so don't know what lenses you use?


So does both the lenses on my canon 350d. Infinity is NOT focus on either of them, but slightly back from infinity is :thumbsupmate:

[omaroo]

on my 70-200 2,8 IS, and 17-40 from canon, infinity works perfect.
on 200 2,8 prime also, and 10-17 from tokina.

so don't know what lenses you use?

If you are apparently reaching perfect focus at the infinity hard-stop then you might have a problem with your setup - because this shouldn't be.

MOST lenses are not focused when cranked around to infinity for any particular body they are mounted to at the time. Infinity focus is usually back a small amount from the end of travel - and this is done on purpose to ensure that you CAN reach infnity focus depending on temperature conditions and the like. Lenses change shape and focal length if they are hot or cold, so a hard mechanically-set position is a really bad thing. Also, by no means are distances from the lens mounting flange back to the film/sensor plane guarranteed to be the same between camera brands or even models within a brand. A reliable hard-focus at the infinity setting isn't unusual, but probably undesired - especially if using generic lenses. Not one of my 12 Nikkor prime lenses reaches focus at the end of travel on any body I have. On a couple (my 300Ed for instance, I have an arrangement of two opposed stainless steel medical grade hose clamps attached so that I can set my typical infinity focus and then adjust the bands so that they hit each other at focus. I use this as a quick guide when setting up - but always go through the whole focus routine using ImagesPlus.

[scorpius]

Good comment omaroo. I have found that most of my Pentax, Canon and Tamron lenses at the end stop go past the maximum focusing point by a smidge enough to start blurring. This occurs on both film and digital camera/lens.
Unless you have 20/20 vision this can be a real bug in photography and probably the only answer is a correction lens prescription eyepiece adapter. I have one for my old Pentax film camera. (which needs updating!)

[ian robbo]

Well, you might use one of those nifty magnifying rightangle viewers that slip onto the SLR viewfinder or use Lifeview (on the little screen on the camera (might be award and you might have to become a contortionist to achieve this , or you can do it via Liveview on the lappy screen using the camera's bundled software - gotta lug a heavy and expensive lappy out and about in the damp dewy night , murder on you night vision too unless you've got some red plastic over the screen .... not healthy for your lappy) and then zoom in on a star and make focusing adjustments until it's as good as you can get.

Best to keep it all light and simple (KISS) I reckon.

BTW : good to see there are still some film dinosaurs like me about .... I've only recently bought a Canon 40D and haven't dipped my toes into the new waters of digital imaging yet .... got a backyard roll off roof obverving shed and a couple of permanent piers (for the Atlux and 10" newt and the old CG5 and the sky patrol rig using my old Minolta XD5) to sort first and it's been to dambed foggy and cloudy lately here in Gateshead,NSW.
Also need to enhance my old CG5 to allow it interface with the Orion Autoguider I recently spashed out on so I can autoguide the old rig. (cf a AWR handpaddle modification ?? I don't need GOTO on the CG5).

Might dust off the old hypering kit and get some forming gas then maybe (been years since I used hypered colour 35mm film) unless I decide to retire the XD5 and maybe get another DSLR for the sky patrol rig.

[Radar]

Hi Ian,


good to see there are still some film dinosaurs like me about

Likewise. I love film. Its been a while since I went bush with it. I had a little boy nine months ago so things have kind of been put on hold. But I'm gearing up to go soon.


Might dust off the old hypering kit and get some forming gas then maybe (been years since I used hypered colour 35mm film)

Been a while since I heard someone say this. Would love to see some photo's of your setup sometime.

Welcome to MyAstroSpace!

Ray

[ian robbo]

Hi Ian,



Likewise. I love film. Its been a while since I went bush with it. I had a little boy nine months ago so things have kind of been put on hold. But I'm gearing up to go soon.



Been a while since I heard someone say this. Would love to see some photo's of your setup sometime.

Welcome to MyAstroSpace!

Ray

I'm an IIS refugee .... don't think much the moderation and attitudes of some people there. Too scared of offending local dealers there too.

Kids , family and work has a habit of buggering up your astroimaging , time just evaporates !!!

1O" home assembled f/4.66 newt is in pieces , upgrading the OTA and modding the new Orion Al Cell. This will be upgrade V3. Started off as a home built dob, then later I got hold of the CG5 and I did some OTA upgrades (V2).

Add designing and then building a roll off roof observing shed in the back yard - boss woman will be glad to see the end of the gems and tripods and telescope stuff and bnps in the spare bedroom when I get that done.

Then I might take a few snappies of the set up (for prosperity and insurance purposes , already had one telescope nicked from my garage (my old Vixen 4" FL APO and GP-DX a couple of years ago).

[Radar]

Observatories are a luxury. I remember many times where I'd want to go outside and do some imaging but I was just too lazy to set everything up. Now it's just a case of sliding the roof to one side. I really need to get a serious CCD camera though. I have an imaging source camera, and a Meade DSI Pro II. I want to get something decent in the coming year. My obs will see some serious photon's once I get a decent deep sky camera.

Shame you had the vixen stolen. Nice scope.

Please post progress photo's of your obs as it comes together.

Ray