Astroscope + eyepiece + compact camera - Setup (2 Viewers)

[cruedag]

Feather detail

Hi,

About feather detail here you have some real pixels crops from the Sony W7 7mpx camera with this setup.

Pictures are directly cropped from original pictures, with no kind of post processing, neither sharpening or any other kind of improvement. With slight post processing the picture will look much better.

I also use prime focus with a reflex and I enjoy each kind of setup for different purposes; the Canon 1000D at prime focus yields crazy good detail with the Televue 76 at near reach, but when you intend to get more reach the compact camera is a real delight.

Real pixels crop, ISO100, F7.1, 1/250s. Equivalent focal length of the shot: 2000mm.

 

[cruedag]

ISO100, 1/250s, F5.6, 1520mm of equivalent focal length.

Again a real pixel crop from the original jpeg captured from the compact camera.

 

[cruedag]

Some other pictures from another session; some of them are cropped, and they are only scaled down with IrfanView (no photoshop or other advanced processing).

The frog is a crop shooted at 3900mm of equivalent focal length. Others are shooted between 1500mm and 2700mm FL.

 

[cruedag]

Same session, some other pictures only cropped and scaled down with IrfanView, FL between 1700mm and 2400mm.

 

[cruedag]

Finally, two more that are processed with PS, some color, exposure and noise improvements. For web publishing sizes the extra processing is not very important.

The rate of good photos with this setup is very high, feeling almost the same that with the standalone P&S camera.

I use the compact camera in multipoint macro AF mode, so it gives the final touch of focusing to the picture... if you don't reach exactly the correct focus with the scope, the camera helps you that little bit more.

Regards

 

[Jim Bennett]

Very nice m8.

 

[DanC.Licks]

7 Mp in a 38mm² sensor is going to give you tons of reach and lots of detail. Where it will fall short is in dynamic range, ISO range, and color rendition.
Your shots are amazingly good for this kind of setup, but the trade-off is also clear. I also feel the best solution is prime focus with either a TN, or good TC for added reach.

 

[cruedag]

Hi Dan. I also use prime focus with different barlows and powermates with the Televue 76 and a Canon 1000D.

After learning how to conveniently baffle them (thanks to the much appreciate help of Paul Corfield) results are also good with my 2x GSO 2'' and my Powermate 2.5x.

But with an APS-C sized DSLR, even with the light that we have in Spain, speed of the shot is not enough to retain all the detail available from the setup in real action.

In a static test results are even better than those showed with the P&S camera, but in the environment where I take most of my pictures, speed is critical with prime focus + teleconverters.

For example, last pictures showed were taken all of them from inside the car, where the tripod doesn't stand as rigidly as needed. Even the car bounces itself. In that situation I don't get the same detail level from prime focus setup when using more than 2000mm EFL.

In a shorter range, for example using a hide, detail level from prime focus setup is really difficult to believe.

I want to test a M4/3 camera (or even better, a Nikon 1 V1) for that purpose: reaching more focal length with a prime focus setup without lossing too much speed in the way.

About dinamic range of the P&S camera, of course is a real downside, but remember that most of the pictures showed are not post processed at all, neither levels adjustment, leaving the levels of the original jpg (not RAW). Previously I had a Sony W5, basically the same camera but with 5 mpx instead of the 7 mpx of the W7. I preferred the results of the W5 because of slightly better dynamic range and noise performance, as expected having less resolution in the same sensor.

Regards

 

[DanC.Licks]

By speed you are talking about shutter speed? So that means you are able to use higher shutter speeds with the P+S?

 

[cruedag]

Yes, I meant shutter speed.

When you send all the light collected from the aperture to that small sensor (coupling afocally) you get much quicker shutter speed operation.

Situation goes even worse when you use teleconverters in your prime focus setup, of course.

Despite of the evident differences in exposure, you can see these two pictures shooted at about the same FL to a neighbourhood 8kms away.

First one, clearly underexposured:
TV76 + Radian 14mm eyepiece + Sony W7 at full zoom. EFL=3900mm.
ISO100, 1/640s, F5.2.

Second one, overexposured:
TV76 + 2x GSO + Powermate 2.5x + prime focus Canon 1000D. EFL=4000mm, more or less.
ISO1600, 1/400s, F5.2.

Despite of the different exposure, pictures' EXIF shows more than 4ev steps between them.

Regards

 

[DanC.Licks]

Hmmmm, might give me something to think about. I shoot 4/3 (E-30) and I am wondering if it would work with say a 35mm 3.5 macro. Trouble is, the only eyepieces I have are 32mm and 42mm, + a 7mm planetary.

 

[cruedag]

Dan, it could work.

With your scope, a 32mm eyepiece, a 35mm macro lens and your M4/3 you'll have:

EFL = 600 / 32 * 2 * 35 = 1312 mm of equivalent focal length

That lense in your camera will work like a 70mm equivalent lense, so if you could attach it at the proper distance from the eyepiece you will have no vigneting at all with an eyepiece with more than 35 degress of AFOV, easy to achieve for most eyepieces. The longer the eye relief of the eyepiece, the easiest to achieve the right distance.

With that setup, coupled afocally, you will have most of the light collected by the scope's aperture covering your sensor.

In a prime focus setup, you are wasting a lot of area with a M4/3 sensor because the coupling could illuminate even a full frame sensor, so with your sensor you are using 4 times less area that what is beign covered by the light gathered by the scope's aperture.

I think that with a well coupled M4/3 lense you'll have more than 1ev advantage over the same focal length obtained with a prime focus setup (1300mm afocally versus 1200mm with prime focus).

Another question is geometric distortion and sharpness, but I'm pretty sure that you'll get better shutter speeds coupling afocally.

P.D: in fact, here in Spain some mates are obtaining great shutter speeds with the Panasonic G1 and some M4/3 lenses.

Regards

 

[Paul Corfield]

On my Canon dslr I tend to get the same shutter speed whether using eyepiece/lens or prime focus with teleconverter.

Here's a couple of images, first image is SW80ED with 17mm Baader Hyperion eyepiece and 50mm camera lens giving around 1750mm before crop factor or 2800mm after crop factor.

The second image is with a home made 3X converter consisting of 5 glass elements. This gives around 1800mm or 2880 after crop factor.

Shutter speed for both was exactly the same. Contrast and detail were better with my home made converter.

Distance was around 85m (279 feet).

Third image shows target with 600mm and no extra mag.

Paul.