Shooting widefield

[Rustang]

I'm thinking this is probably a stupid question and that I already know the answer but in regards to setting up to shoot widefield with a DSLR and lens, if I set a plate solve profile for that setup I can then use APT and PHD2 the same way I've been using it!? Is there anything I need to know that's not already obvious!? I'm guessing I would have to set up an individual profile for each possible focal length in order to plate solve but in regards to that, I'm not sure what focal length that maybe especially if I get a telephoto lens such as a 55-250mm, it seems a bit of a faff. It's only because I'm toying with the idea of getting a lens to do some wide shots, hopefully of Orion before it begins to disappear. 

Edited February 13, 2021 by Rustang

[alacant]

Hi

Yeah, it's the same as using a telescope. Just enter the focal length.

But bear in mind that a typical zoom lens at 55mm (to fit in the whole of Orion) has an aperture of only 12mm; painfully slow. Which probably explains why 12mm f4.5 refractors never caught on!

Cheers

[Rustang]

2 minutes ago, alacant said:

Hi

Yeah, it's the same as using a telescope. Just enter the focal length.

But bear in mind that a typical zoom lens at 55mm (to fit in the whole of Orion) has an aperture of only 12mm; painfully slow. Which probably explains why 12mm f4.5 refractors never caught on!

Cheers

Ok now you have me confused!? Easy done! lol

[alacant]

1 minute ago, Rustang said:

confused

Short version: your lens has a focal length of 55mm. Enter that value in PointCraft instead of your current telescope focal length.

 

[Rustang]

5 minutes ago, alacant said:

Short version: your lens has a focal length of 55mm. Enter that value in PointCraft instead of your current telescope focal length.

 

Its the 55mm has only an aperture of 12mm!? that would be good to understand before i spend out on a lens! 👍

Edited February 13, 2021 by Rustang

[alacant]

34 minutes ago, Rustang said:

55mm has only an aperture of 12mm!? that would be good to understand before

A typical (affordable?) 55-200 zoom has a maximum f-ratio of 4.5.

Maths: 55/4.5 = 12.2

But don't let that put you off. Many of us put up with it. Worse, even; you'll have to close the aperture even smaller to get decent stars. Frightening eh?!

Cheers

[Rustang]

1 minute ago, alacant said:

A typical (affordable?) 55-200 zoom has a maximum f-ratio of 4.5.

Maths: 55/4.5 = 12.2

But don't let that put you off. Many of us put up with it. Worse, even; you'll have to close the aperture even smaller to get decent stars. Frightening eh?!

Cheers

Apologies, I get it now, I forgot that a camera lens has aperture blades which I'm guessing is what you mean buy it going down to a 12.2 aperture!? 

[alacant]

13 minutes ago, Rustang said:

aperture blades

No, not due to the blades as they will be fully open. At 55mm, 12.2mm is the maximum opening.

Edited February 13, 2021 by alacant

[Rustang]

3 minutes ago, alacant said:

No, not due to the blades as they will be fully open. 12.2mm is the maximum opening.

Apologies, I'm really showing my dumbness now! No wonder I struggle with this hobby! 😊 So the rear opening of the lens then!? 

[alacant]

No. The maximum opening of the lens. This corresponds to the minimum clear diameter of the lens cell along the light path. In this case 12.2mm.

if it helps, look through a lens as you zoom. You'll see the aperture change as the focal length changes. At 200mm, the aperture is larger so as to keep the f-ratio at f4.5. In fact some zoom lenses can't manage to keep the f-ratio the same and can quite often offer a smaller ratio for the longer focal lengths. E.g. 55-300mm f4.5-5.6.

HTH

Edited February 13, 2021 by alacant

[Rustang]

7 minutes ago, alacant said:

No. The maximum opening of the lens. This corresponds to the minimum clear diameter of the lens cell along the light path. In this case 12.2mm.

if it helps, look through a lens as you zoom. You'll see the aperture change as the focal length changes. At 200mm, the aperture is larger so as to keep the f-ratio at f4.5. In fact some zoom lenses can't manage to keep the f-ratio the same and can quite often offer a smaller aperture for the longer focal lengths. E.g. 55-300mm f4.5-5.6.

HTH

Ok I see, I didn't know that's how a camera lens functions. Thanks for the info. One last thing while I think about what to do. For the plate solving, I remember setting up the profiles for the scopes and cameras I have for APT to be able to plate solve. You mentioned about entering the value in point craft, would I not have to set up that profile as well so in regards to a zoom lens which could be many different focal lengths, would I then have to set up profile for each if that makes sense!? If that's the case I guess it would be easier to stick with a fixed focal length lens. 

[alacant]

13 minutes ago, Rustang said:

fixed focal length lens

I've only tried a zoom once; a 75-300mm which came as part of the 700d bundle. It's ok as a daytime lens but no good for astrophotography. Well, not with me in charge of it that is. 

We've just posted an example with a fixed 135mm lens. They can be picked up cheaply and I can recommend this as a possible route into what you want to achieve. It also makes your apt profiles manageable.

HTH

[Rustang]

13 minutes ago, alacant said:

I've only tried a zoom once; a 75-300mm which came as part of the 700d bundle. It's ok as a daytime lens but no good for astrophotography. Well, not with me in charge of it that is. 

We've just posted an example with a fixed 135mm lens. They can be picked up cheaply and I can recommend this as a possible route into what you want to achieve. It also makes your apt profiles manageable.

HTH

Yeah saw that, turned out well. Certainly an option as I can't afford the Samyang! I was after a cheap bit of fun myself just to try something different. 

What was the adapter you used to fit the newer canon body or was it a straight fit for EF /EF-S bodies!? 

Edited February 13, 2021 by Rustang

[alacant]

34 minutes ago, Rustang said:

the adapter

https://a.aliexpress.com/_uHxrd1