Please help with focusing!

[alpha015]

Hi,

Please help. I'm using a 135 2.8 pentacon and a 120 MM asi zwo, but i can't focus, neither to something close nor distant.

I just see plain black gray or white, regardless of what settings I change in the lens and camera.

[Tim]

Hi,

Have you set the correct distance between camera lens and the imaging chip?

[alpha015]

1 minute ago, Tim said:

Hi,

Have you set the correct distance between camera lens and the imaging chip?

Thanks for your answer.

Nop, I have no idea.

Nothing said about it in the intructions sheet of the camera.

[Tim]

Give me a sec I'll try and find the info you need

[Tim]

How are you attaching it to the camera? Maybe a pic from a phone to show us etc?

[Tim]

Specifically, what lens mount does the lens have? You need this to find the correct flange to film measurement for the lens, and then set that as the distance between the back flange on the lens and the image sensor on your ASI

[Tim]

Here's an old thread which may help

 

[alpha015]

1 hour ago, Tim said:

How are you attaching it to the camera? Maybe a pic from a phone to show us etc?

 

[alpha015]

1 hour ago, Tim said:

Specifically, what lens mount does the lens have? You need this to find the correct flange to film measurement for the lens, and then set that as the distance between the back flange on the lens and the image sensor on your ASI

M42

[alpha015]

1 hour ago, Tim said:

Here's an old thread which may help

 

Thanks!

I think the back focus distance of the zwo is 12.5mm and i guess the pentacon flange focal distance is 45.46 mm.

But, what would I need ?

[Tim]

Normally an M42 > T Thread adapter (assuming the ASI has a T Thread (M42 X 0.75) thread??, preferably 35mm in length. If you have shorter, you can extend with spacers, but a proper sized one is best.

Camera M42 threads dont screw into T Thread fittings!

[alpha015]

1 hour ago, Tim said:

Normally an M42 > T Thread adapter (assuming the ASI has a T Thread (M42 X 0.75) thread??, preferably 35mm in length. If you have shorter, you can extend with spacers, but a proper sized one is best.

Camera M42 threads dont screw into T Thread fittings!

yes, the camera came with a 35 mm T thread 

in the topic thread you sent me I read 'The Pentacon M42 thread is NOT compatible with the M42 'T' thread standard'

could you please provide me a link to what exactly I need to buy?

sorry about my ignorance

 

[Tim]

You need something like this

https://www.365astronomy.com/TS-M42x1-female-to-T2-male-adapter-for-Russian-Objectives.html

You may be able to find one with the correct optical length, or may need extra spacers.

The lens has a male 42 x 1mm thread, and the female thread on the camera is 42mm x 0.75, the adapter makes them compatible.

 

 

[happy-kat]

This is a great reference page for different camera flange focusing distances when using a lens from a SLR camera.

link here

[alpha015]

5 hours ago, Tim said:

You need something like this

https://www.365astronomy.com/TS-M42x1-female-to-T2-male-adapter-for-Russian-Objectives.html

You may be able to find one with the correct optical length, or may need extra spacers.

The lens has a male 42 x 1mm thread, and the female thread on the camera is 42mm x 0.75, the adapter makes them compatible.

 

 

Thank you! by the correct optical lenght do you mean that I need either one of those 35 mm long or one of those plus a T2 (35-7=28) 28 mm long?

 

[alpha015]

2 hours ago, happy-kat said:

This is a great reference page for different camera flange focusing distances when using a lens from a SLR camera.

link here

Thanks! for the M42 it says: 

On bodies with a flange focal distance greater than that of M42, most notably Nikon, three options are available. A simple mechanical adaptor allows the lens to be mounted, but the effect is similar to the introduction of an extension tube, reducing the minimum focus distance at the expense of losing infinity focus. Alternatively, an adaptor with an optical element can be used to retain the original focus range of the lens, at the expense of some image quality. Finally, it is possible to replace the M42 mount on some lenses with the desired camera mount, or to perform the reverse change on a camera body.

The backfocus of the zwo asi 120MM is 12.5 mm .. so I guess I shouldn't be having any problem?

[happy-kat]

My own in hand testing of different lenses on my Meximage 5 camera is that the distance the camera needs to be from the lens is what ever the flange distance was for the camera the lens was designed/used on originally. I do not think you need any adapter with an optical piece you just need to get the spacing right for the gap from your camera to the back of the lens you have using a straight through adapter..

For example Canon lenses will reach infinity focus with an M42 lens. Canon will reach focus with a Nikon lens (with straight through adapter). Nikon wont reach focus with either a Canon or M42 lens because the flange distance for a Nikon is shorted than for a Canon or the original Pentax SLRS the M42 mount was on..

 

[alpha015]

3 hours ago, happy-kat said:

My own in hand testing of different lenses on my Meximage 5 camera is that the distance the camera needs to be from the lens is what ever the flange distance was for the camera the lens was designed/used on originally. I do not think you need any adapter with an optical piece you just need to get the spacing right for the gap from your camera to the back of the lens you have using a straight through adapter..

For example Canon lenses will reach infinity focus with an M42 lens. Canon will reach focus with a Nikon lens (with straight through adapter). Nikon wont reach focus with either a Canon or M42 lens because the flange distance for a Nikon is shorted than for a Canon or the original Pentax SLRS the M42 mount was on..

 

thanks for your answer!

my lens seems to focus at infinity focal 2.8 with the 35 mm T2 that came with the camera

i pointed to buildings that are like 1 km away

but! the T2 that came with the camera is thought for an eyepiece, one of its sides don't screw into the pentacon i just put it close to the M42 mount of the pentacon, but cannot be screwed

do i have to buy a proper T2 that i can screw to the pentacon or without screwing it will equally work?

[happy-kat]

I would imagine that if you hold securely with no movement the camera and the lens in the right place then all you might do is for example using flocked card or say flocked plastic wrap that around the lens barrel and camera side to ensure there is no light getting in. That would be the cheapest solution.

[alpha015]

6 minutes ago, happy-kat said:

I would imagine that if you hold securely with no movement the camera and the lens in the right place then all you might do is for example using flocked card or say flocked plastic wrap that around the lens barrel and camera side to ensure there is no light getting in. That would be the cheapest solution.

great idea, thanks!

will probably get the ring extensor though

[happy-kat]

It wont be water tight so be careful of any dew forming on your camera. I proper fitting would be best and secure.

 

Hopefully someone will respond with their solution because there are others using old m42 lens mainly Takumar lenses to cameras like your fitting.

[happy-kat]

Not saying this is the same solution as your camera but if your Pentacon lens has the standard camera m42 mount then you might be best searching for use of a camera like your one to a Takumar lens (they often have a camera m42 mount likely the same as I think your Pentacon but the Takumars are a popular vintage lens to use so come up more in searches).

link here

another link

link here

 

[Lonestar70]

9 hours ago, happy-kat said:

 

For example Canon lenses will reach infinity focus with an M42 lens. Canon will reach focus with a Nikon lens (with straight through adapter). Nikon wont reach focus with either a Canon or M42 lens because the flange distance for a Nikon is shorted than for a Canon or the original Pentax SLRS the M42 mount was on..

 

I think you will find it is the other way round Happy-Kat...

The Flange focal distance for Nikon cameras is 46.5mm which is longer than the 44mm for the Canon.

This is why the Canon can use a Nikon lens with a straight through adapter which increases the distance between the lens and the camera sensor.

The Canon lenses won't work with a Nikon camera as they are designed for the shorter 44mm flange focal distance.

[happy-kat]

Yes thank you, I did get it the wrong way around.

[MarsG76]

On 21/05/2018 at 18:20, happy-kat said:

Yes thank you, I did get it the wrong way around.

Look at that.. something so small and simple and such a big effect on the optics...