Canon 300 2.8 II

[smr]

Hi,

Just wondering if anyone has one of these Lenses for Astrophotography. Apparantly the mk1 version isn't very good for AP according to Jerry Rodriguez and his tests with it.

I can't find much info on the mk2 Lens though. At such an extreme focal length and aperture combo I've heard that focus is more difficult... is it possible to use an electronic focuser with these big prime lenses ?

[nfotis]

At least, Astromechanics has an ascom compatible focuser for EF lenses.

Another possibility is to use a follow focus ring and handle.

N.F.

[smr]

2 hours ago, nfotis said:

At least, Astromechanics has an ascom compatible focuser for EF lenses.

Another possibility is to use a follow focus ring and handle.

N.F.

Thanks. Hadn't heard of that before. Looks like it would work great. Would it be able to autofocus for temperature drops. ie. connect it up and leave an imaging session running for 6 hours unattended? 

I suppose if that covers the focusing and autofocus solution it just leaves the question as to whether the lens is optically sound for astro. 

I know it is for terrestrial photography. It's probably the sharpest Lens Canon have ever made.

The reason I am wondering about the suitability for AP is because I have been thinking about buying this Lens for wildlife, landscape and sport quite a lot over the past year but didn't get around to it.

If the lens is suitable for AP it could be worthwhile investing in as I could also buy a 2X Extender and then get 420mm at f/4.

[Seelive]

28 minutes ago, smr said:

... I could also buy a 2X Extender and then get 420mm at f/4.

I assume you really mean the x1.4 extender.

[Seelive]

Clarkvision.com appears to rate the Canon 300 F2.8 Mk2 for astrophotography but personally I have never used one (way above my budget), however I do use the Canon 200mm F2.8  and the 400mm F5.6, both of which I rate highly for astrophotography.

Edited January 29, 2021 by Seelive
Typo

[nfotis]

Since I own the 400/5.6L, doing a good focusing would be nice (and avoid buying a dedicated telescope like an Askar 400).

One possibility is this Astromechanics adaptor I mentioned. Theoretically, it should give the most accurate focusing mechanism, since you can use the  smallest possible step of the USM motors. Another (cheaper) option would be a follow focus ring, that would be a first approximation (the aperture could be controlled from a Canon DSLR - you do a 'depth of field' confirmation check with the dedicated button, then remove the lens while you keep pressed this button, and you have the aperture fixed for the astro camera)

N.F.

 

[nfotis]

On 29/01/2021 at 20:07, smr said:

Thanks. Hadn't heard of that before. Looks like it would work great. Would it be able to autofocus for temperature drops. ie. connect it up and leave an imaging session running for 6 hours unattended? 

I suppose if that covers the focusing and autofocus solution it just leaves the question as to whether the lens is optically sound for astro. 

I know it is for terrestrial photography. It's probably the sharpest Lens Canon have ever made.

The reason I am wondering about the suitability for AP is because I have been thinking about buying this Lens for wildlife, landscape and sport quite a lot over the past year but didn't get around to it.

If the lens is suitable for AP it could be worthwhile investing in as I could also buy a 2X Extender and then get 420mm at f/4.

 

I haven't used this adaptor myself, but I cannot see why it won't work (I don't remember where it draws the power for operation, I would guess via the micro USB connector?)

If you check the page https://astromechanics.org/ascom.html , you should notice that there are multiple versions of this adapter, due to the needed thickness of different astro cameras. Check also the various PDF pages for each adapter available. The most typical example is the M42 version: https://astromechanics.org/downloads/ascom_ef/en/manual/controller_m42.pdf 

 

N.F.

[Seelive]

4 minutes ago, nfotis said:

Since I own the 400/5.6L, doing a good focusing would be nice (and avoid buying a dedicated telescope like an Askar 400).

One possibility is this Astromechanics adaptor I mentioned. Theoretically, it should give the most accurate focusing mechanism, since you can use the  smallest possible step of the USM motors. Another (cheaper) option would be a follow focus ring, that would be a first approximation (the aperture could be controlled from a Canon DSLR - you do a 'depth of field' confirmation check with the dedicated button, then remove the lens while you keep pressed this button, and you have the aperture fixed for the astro camera)

N.F.

 

I've never had a problem focusing using liveview at x10 but I can see that focusing at x1 could be a delicate operation.