SW 80ed vs 300mm f4 camera lens

[idigitize]

Attaching a 0.85 focal reducer to the 80ed 600mm bring it to f6.3 at 510mm

I have a 300mm f4 with a 1.7 teleconverter strangely enough is also 510mm at f6.7.

Is there anything special the scope will give me over the lens I'm missing?

For wide view dso, I'm assuming they would be identical?

I guess putting the 1.7tc on the ed80 would be an option to give me a1000mm which would be nice for some lunar shots if that works?

I'm almost thinking that a 80ed is almost pointless as I own the 300 and 1.7' already?

[Naemeth]

If they perform to the same optical standard, then you are right there is no need for the scope if you are just using it photographically. Normally it's the other way around, the scope (sometimes cheaper than an equivalent lens) replaces the lens .

[idigitize]

Thanks, I wasn't sure if CA or any other things would be better/worse. 

[davew]

How your lens will work depends very much on the lens I think. If you are referring to the latest Canon 300mm f4 then the images I've seen are very good indeed.

Not so sure about the converter but there's only one way to find out..........

Dave.

[idigitize]

its a Nikon 300f4, regarded as a very good lens. The 1.7 is a good TC, but recommended to stop it down when in use to get optimum performance.

Will have to give it a go I guess. 

[ollypenrice]

You need to see how the lens does. It might be very good, especially if it will give crisp edge stars when wide open. However, if you need to stop it down than I'd use a front aperture mask to avoid diff artefacts. They're easy to make.

When you focus, stick strictly to Psychobilly's advice and put your focus star at one of the intersections of the 1/3 lines. This will give a larger well focused field.

Olly

[davew]

Yep, the Nikon 300mm should do it especially if it's the AFS version.

The converters are very much lens dependant I feel. Some lenses react very well and others don't. To stop down would make your task more difficult unless you have particularly good guiding. You'd also get star spikes that you'll either love or hate

One thing to note though. I wouldn't mount it with the tripod collar. Try and use a large guide ring if you can.

Dave.

Edit. Cross post !

[idigitize]

thanks for the heads up!   when you say 'large guide ring' do you mean like a couple of tube rings round the lens? sorry for the thick question.

[Psychobilly]

I know Photosbykev and myself have both mounted his (now mine) Canon 600/f4L IS USM by it's collar... using a medium dovetail using both the 1/4"  and 3/8" attachment points... I have also use the tripod collar for a 300/2.8...

I have only just modded my outdoor pier to take the EQ6 so haven't used them in anger yet...

Peter...

[davew]

Yours isn't the 300mm f4 Nikon.

I don't say this lightly but I won't say any more

Dave.

[davew]

thanks for the heads up!   when you say 'large guide ring' do you mean like a couple of tube rings round the lens? sorry for the thick question.

You can try the collar if you wish but with this lens I would try and stabilize it with one of the larger guide rings near the front. We wouldn't want the lens flopping about in a collar that would be a disgrace on a 30mm lens,

Dave.

[laser_jock99]

Star photography is the most critical test for a camara lens. Sometimes they are okay- but more often not. Sperical abberation, chromatic aberation and internal reflections being common problems. In some ways telescopes are better because they have simple light paths with fewer optical surfaces (six at the most with an apo triplet).

As has been said it's worth a try but my expaectations would not be that high. I have a highly reviewed Sigma ED 300mm F2.8 lens- which is great in normal use- but I don't use for astro any more as the corner stars are always eliptical up to F5.6 past which I'm in refractor F number territory.

[Psychobilly]

Yours isn't the 300mm f4 Nikon.

I don't say this lightly but I won't say any more

Dave.

As a "tog" with a foot in both Nikon and Canon Camps I am "horrified"...

Peter...

[idigitize]

The lens collar on the Nikon 300f4 has always been topic for debate anyway, let alone trusting it upside down whilst trying to focus and remembering on the d800 the zoom in and zoom out buttons have been reversed.

I will look forward to trying to focus on a star, the weather is looking so encouraging at the moment...not!