Field Corrector for Newtonians and D=50mm field diameter

Description

The corrector was designed for the larger format CCD-camera (especially with one eye on the new SBIG series) to cover a larger field than possible with a 2” corrector. It should be clear, that 2”, with a clear aperture of maybe 40mm, cannot cover a field of 40mm with an f/4 light cone. Therefore, a 3” barrel was chosen to cover field diameters of up to 50mm with low vignetting. The backfocus is large enough (appr. 59mm) to use most known CCD-Cameras with filter wheels. The corrector ends with a flange with 6xM3 Threads on D=68.5mm. Adapters can be ordered for several cameras. Please note, that the corrector does not use cheap 3xBK7 glasses like other correctors and it does not increase the focal length ! Expensive glasses have been chosen, to minimize the corrector length, minimize the spot-size but maximize the back-focus for easy use of filterwheels.

Examples

The corrector can be used between f/3.5 and f/5.5. The corrector has been optimized for a field diameter of max. 50mm. In the below examples you can see the performance and vignetting (assuming that you use a large enough secondary mirror) for different examples. The box-size of the spotdiagrams is 0.02mm (20 microns). The wavelengthrange for the calculation of the spots have been from 400nm to 700nm. Spots and vignetting are shown for a D=44mm field

300mm f/4 Spotsizes	300mm f/4 Vignetting
400mm f/3.5 Spotsizes	400mm f/3.5 Vignetting
400mm f/5 Spotsizes	400mm f/5 Vignetting

as can be seen from the calculations, the same corrector can be used on a large range of Newtonian mirrors from 250mm to 1m diameter. Spotsize is very small, concentrating 80% in 1 Pixel even for cameras with small pixel size.

Drawing and Distances

Please note the following distances for different mirrors:

A=Distance from Flange to Focus

B=Distance from Flange to primary mirror vertex (middle of the reflecting surface)

Price:

The prices is 790 Euro net ex Germany. If you are european community you have to add 16% VAT. We try to have this corrector on stock, but the demand is so strong that our manufacturers are now back on schedule so there is a waiting time of 2 months.

How to order:
Since we are specialized on telescopes >400mm and in the last months we have been flooded with requests and questions about our correctors we have passed the distribution of these correctors to AstroSysteme Austria. If you have questions about this corrector or you want to order, please contact

www.astrosysteme.at

Astro Systeme Austria, Grünbach 81, A- 4264 Grünbach/Österreich
Geschäftsleiter: Egon Döberl, Telefon: +43/0/6643327965,
E-mail: egond@gmx.at

They also sell great ready-to-go telescopes that use these correctors !

Ghost Problem with the Wynne-Corrector

Some people recently have reported about ghost images of bright stars which are on the opposite side of the star.
Brian Lula has made an example image of such a ghost on a mag 6 star.

http://www.heavensgloryobservatory.com/Color_Jpegs/m3b&w01.jpg

the ghost images are created by a 2x reflection from the CCD sensore or cover slip with the back side of the first lens. The diameter of the ghost is appr. 1.5mm. Always if I design a corrector I try to make ghost images >1mm diameter so the intensity is so weak that they can't be seen. The lens reflects about 0.5% of the light.

In the case of some CCD's like the STL11k with cover slip, the CCD reflects back a lot of light. The most reflections happen in infrared. Therefore, you can reduce the ghosting significantly (by about 2 magnitudes) if you use an IR Block. Also cameras without cover slip don't have the ghosting problems or they only appear on really bright stars.

Cord Scholz made test images of M13 with a STL with and without IR Filter.

M 13 without IR-Block Filter

M 13 with IR-Block Filter

So some conclusions:

Every glass air surface causes reflections. If you see or not see the ghost depends on how out of focus the ghosts are. Smaller ghosts are easier to remove (by median filtering), bigger ghosts appear only on brighter stars

Since the Wynne has 6 surfaces, every surface can produce ghosts and under some conditions you may see them

There is nothing wrong with the coating or anything else with the corrector as some people have suggested.

People have used the corrector more than 1.5 years before the first noticed that there can be a ghosting problem.

You can reduce the ghosting significantly by using an IR Block filter, but on very bright starts you will still see them

Cameras with cover slip give stronger ghosting than cameras without cover slip

You can remove the ghosts if you move the image and make a median filter. You might need this if you try objects like the plejades etc.

If you think that this is a disadvantage that you don't want to accept please DO NOT BUY IT

If you have received the corrector and you are happy with the pin point images but you are uncertain about the ghosts you may never see PLEASE SEND IT BACK and we will immediatly refund the money.