Shooting wide field, not getting much signal

[Spookyer]

:help:I have put a 70-200mm f4 camera lens on my STT8300 for the first time and I am shooting Rho Ophiuchi at 70mm. Even with a 10min sub I am getting very little nebulosity on the Lum and now the Red filters, can see the stars fine but can barely see M4. Can only just tell it is a cluster.

Am I doing something wrong?:help:

Brett

[MrB]

Strange. If it's an AF lens(doesn't have the aperture ring that manual lenses have), have you checked it's not stopped down to f16 or something stupid*?
I'm pretty sure Canon's are wide open when there's no power on them, the few I have are anyway, but different brands may behave differently(yours is a Nikon?) worth checking anyway.

Edit: *stupid f-ratio, not you stupid ;)

[Octane]

Yeah, most likely your lens is stopped down.

Are you getting diffraction spikes on the brights stars, such as Antares? That would be a giveaway.

On Canon lenses, if you wish to stop them down (they're natively wide open, as Simon wrote), you close down to the desired aperture, press the depth-of-field preview button, then, take the lens off the camera. It will then be stuck at whatever aperture was chosen.

It's perfectly safe to do it on Canon lenses, but, I don't know anything about Nikon.

H

[multiweb]

:lol: I had that same issue first time I did widefields with a lens. The lens iris was closed.

[Spookyer]

I had considered that but the lens iris should be wide open except when you actually take a shot. So when I took it off my D4 the lens should have been wide open. Nothing should have changed between then and sticking on the CCD but I will check as it would explain the results.

Brett

[Spookyer]

Okay, after some research I see my assumption was wrong. All of the newer nikon afs lenses have a spring that closes the aperture down when you take them off the camera. Now I have to find a way of opening them up when mounting on the CCD.

Nothing is ever easy.

Any nikon lens shooters out there?

How are you getting over the aperture issue when using them with a CCD camera?

Brett

[Peter.M]

Found this online, I have however never attempted it.

"Nikon G lenses physically needs the aperture feeler to be holing it in place to stay open. Look for a tab sticking out at the rear of your lens; it should be in a slot and it slides about inch or so. Locate it and move it with your finger check to see if it controls the aperture blades, if so you could lock the aperture at any setting by inserting a small slim made of folded paper or a piece of business card or anything similar that will snugly fit in. Remember it should not be loose so that it slides off and not too tight so that it damages the lens."

[Peter.M]

So I have a nikon lens near me with one of these spring loaded latches on it for the aperture. I dont think it would be too hard to get it to stay open for the STT.

[Spookyer]

Thanks Peter, I will look into that.

Brett

[ZeroID]

KM lenses are the same, closed is 'normal'.

[PeterEde]

Another reason to go Canon ;)

[ZeroID]

Nyah !!! I get 12 fps @ 24 megapixels, brill for motorsports :thumbsup:

I would like Live View though, I have considered buying a Canon just for that reason. But I resisted !!! :D

[PeterEde]

I use live view to focus at 10x
Can't imagine focusing through a viewfinder now

[Spookyer]

I have cut a little piece of plastic off the sprue of a plastic model kit to suit. I have inserted it into the gap created when you move the aperture lever open manually. Seems to stay in okay. I will give it a go if I ever see stars again.

Brett