Nikon D3100

[TimB]

Hi. I'm trying to get a focused imaged using my Nikon D3100 DSLR. This camera works perfectly for everything till i try to take a picture through my telescope.

This is what i have.

SW 127 Mak

T2 adaptor to connect the camera directly OTA back.

Celestron 1.25 2x barlow/T adaptor

I set the camera to manual and focus on a distant tv aerial/ chimney pot while looking through the camera eyepiece. The image i see is perfectly focused. Obviously focusing is achieved with the OTA focuser. I take the picture, but the resulting image is quite out of focus. I've tried with the Celestron T adaptor (as an extender) with and without the barlow lens, but no difference.

I sure i'm making a rookie mistake.

Thanks for any help

Tim 

 

[Merlin66]

Tim,

start without the Barlow....

How do achieve focus on the stars. There will be a significant change in focal position between your distant chimney and the astronomical objects.

Also the exposures required will be much greater.

[TimB]

Hi. Thanks for your reply.

So through the OTA the camera eyepiece doesn't show proper focus on near terrestrial objects? Is that the case?

I just assumed that the eyepiece on a DSLR shows exactly what the sensor chip sees/picks up. Is this not quite the case when it's usual lens is removed and replaced by a telescope like mine?

I've got lots to learn and i'm enjoying it too. Crazy weather today.

Thanks

Tim

[ronin]

Distant chinmey pot is not that far away, you need a couple of miles at least and preferably something like the moon which is a bit further. I would say that the viewfinder "should" be a match to the sensor but these days the viewfinder is getting less relevance so may not be. Most people seem to rely 100% on the autofocus and the rear view screen but not the viewfinder. Can eventually see one day that a camera will be offered without one, if it is not already done.

One other slight item is your eyes, even if they are a little off of perfect then you will adjust the focus to compensate and get the best for your eyes, it may be small enough that no-one would ever suggest glasses but it could be present.  The tolerances used are generally very small. Nothing is overly easy.

[jACK101]

2 hours ago, TimB said:

Hi. I'm trying to get a focused imaged using my Nikon D3100 DSLR. This camera works perfectly for everything till i try to take a picture through my telescope.

This is what i have.

SW 127 Mak

T2 adaptor to connect the camera directly OTA back.

Celestron 1.25 2x barlow/T adaptor

I set the camera to manual and focus on a distant tv aerial/ chimney pot while looking through the camera eyepiece. The image i see is perfectly focused. Obviously focusing is achieved with the OTA focuser. I take the picture, but the resulting image is quite out of focus. I've tried with the Celestron T adaptor (as an extender) with and without the barlow lens, but no difference.

I sure i'm making a rookie mistake.

Thanks for any help

Tim 

 

Hi,

 

I use a Nikon D3200 which is very similar to your camera. I use the viewfinder when hooked up to my telescope and it works OK. What shutter speed are you using. It is possible that what you are seeing is movement of your telescope set up resulting in a fuzzy image.

Note that the D3200 and probably also your 3100 cannot use liveview when the lens is detached. The camera does not recognise my telescope and this can be a nuisance.

Try as high a shutter speed as you can and if the result is in sharp focus you will have identified the reason. Try also to use an electronic release instead of pressing the shutter.

The moon is an excellent subject to practise on, particularly when at half moon when you get sharp definition over the boundary between light and dark areas.

 

Jack

[SonnyE]

Use a 2 second delay on the shutter release. That will let the mirror flip up, give it time to settle, then take the image.

Also, use an Intervalometer so you don't have to touch the camera.

 

[Mognet]

Hi Tim

You haven't really made a rookie mistake, but have run into things that don't make themselves obvious with visual observation.

I have an almost identical setup, and I think you might be seeing the effects of two things. The mak 127 has a long focal length (1500mm) so is sensitive to vibration. It can take a few seconds for vibrations from even gentle touches to settle out. For this, use either the 10 second delay timer, or a remote shutter release. You can see this physical movement when zooming in on live view to get the focus. Using a barlow lens will also make this movement appear worse as it will double or treble the focal length.

The other is could be the movement in the air itself, where slight and moving changes to air temperature cause the image to shift. It's heat haze on a small scale, but will still interfere with focus in a photo, even if the focus is sharp in the live view.

I took these two photos. The first is in my sheltered garden at not much more than the minimum focus distance of the mak, 1/15th of a second at ISO 100. It's almost sharp, and I could probably improve on it. The second was a couple of hundred metres away over houses, at 1/320th of a second, ISO 1600. I had to use those settings as the air was moving too much to give a sharp image at a slower shutter speed.

[TimB]

Hi. Thanks for your help.

I've finally made some progress. Still with TV aerials alas, no moon shots. So with changing ISO up to 3200, shutter at 1/2000 and 10 second timer I get an in focus TV aerial at last.  Spectacles on or off made no difference I could discern. 

Still waiting for a clear moon.

Tim

[Mognet]

Glad to hear you are getting there

I've got a clear sky at the moment, which wasn't forecast, so I'm making the most of it and trying the moon shots myself. This is from about 9.25 this evening in the twilight. To focus, I used live view and not the viewfinder, so I could zoom in and get it into reasonably sharp focus (for anyone with a similar camera who has never tried it, that's the Lv switch, and the + and - buttons on the left). Once I got focus I zoomed out again to reposition, then used the 10 second timer.

The camera was setup as 1/320th of a second, ISO 1600, but this can be varied for exposure. I shot in camera raw mode and only performed rough processing and de-noising in RawTherapee. My exposure and processing are a bit off, but it shows that it can be done

[TimB]

Nice moon shot. My D3100 has no LV button and only live view in Guide mode, we're thinking of upgrading camera body sometime soon to another Nikon so everything else still fits. I'm only ever going to be a visual observer except for a few snaps of brighter objects in the sky and hopefully no more of the neighbor's TV aerials for the album 

Thanks

Tim

 

[Mognet]

Thanks Tim. When the sky clears again, I'll do a proper multishot one with stacking in AS!2. The mak 127 seems to pull out a little more detail on the craters than the 200p dob

 

Live view is a switch rather than a button. It's on the back, just off the top right of the screen. I don't know if there were multiple versions of the D3100 with some omitting the live view switch though. I've pulled this from the manual on the Nikon site

 

[TimB]

Ah yes. Found the live view switch now! Thanks for the info. Finally got a moon pic this evening. Played around with ISOs and shutter speeds. This pic is at ISO 1600 and shutter 1/640. 

Yay!

[Mognet]

Glad you've got it sorted now. Have fun!