Jack Schmidling Productions, Inc.
18016 Church Road ~ Marengo IL 60152


NOTE: This page is maintained for informational purposes only. We no longer offer this product for sale.

[picture of EASYTESTER]

The EASYTESTER is an eyepiece-like device that allows the owner or user of any type of telescope to quickly determine the quality of the optical train with no previous experience or skills.

Anyone who has ever purchased or built a telescope has experienced that uncertain feeling of not knowing whether those un-textbook-like images are the fault of the optics, faulty adjustments or just seeing conditions.

The EASYTESTER consists of a classical Ronchi grating mounted in a standard 1-1/4" eyepiece tube. When the device is focused on a bright star, a pattern of parallel lines appears that can be used to determine the optical quality of the system and identify many of the common faults that plague commercial telescopes these days. If the lines are straight and parallel to the edge,one can conclude that the mirror or objective lens is well figured and that the secondary (and) corrector plate are properly figured. If the lines appear to be anything other than straight and parallel, a quick comparison to the defect chart, will identify the type of error involved.

[ideal image][defect image]
Ideal OpticsTypical Defect

The EASYTESTER has many uses in addition to verifying the quality of purchased telescopes. Many folks bring their newly made scopes to star parties to get expert opinions on their labor of love and welcome inputs. Some don't welcome such inputs so you need to be a little diplomatic here because the EASYTESTER makes an "expert" out of anyone who has one.

Although the standard "star test" is probably still the most precise test, it is very difficult for the inexperienced observer to comprehend and very subject to mis-interpretation. Furthermore, unless seeing conditions are excellent, even experienced "star testers" can learn little from the dancing images. The EASYTESTER, on the other hand, will tell its story under the most dismal of conditions, including fog, haze, turbulence, bright lights and full moon.

The EASYTESTER consists of a 133 line grating mounted in a 1 1/4" diameter tube made of instrument quality brass and a plastic eye cap. The grating can be moved up or down and locked into position with a setscrew to accommodate various backfocal distances.


NOTE: This page is maintained for informational purposes only. We no longer offer this product for sale.

Jack Schmidling Productions, Inc.
18016 Church Road ~ Marengo IL 60152
~ Email: jack@schmidling.com


Email received Aug 2003

Mr Schmidling,

Back in December of 2002 I sent you email. I was having trouble interpreting a pattern I saw in your EasyTester when I used it on my 16-inch Meade Starfinder.

You said, "clearly something is wrong with the edge".

I recently sent the mirror off to be tested at Pegasus Optics. Mr. Hall said that the central 14 inches were fine but that the outer 1 inch of the mirror was severely undercorrected and basically contributed noise and no usable light to the image.

I thought you might want to know that your tester picked up this problem, described it correctly (interior good, edge very bad) and let me see it easily! I'm sure you know your tester works, but now you know it works even when used by a new-comer to astronomy.

Thanks for helping me find a real problem,

-John Bishop
Nashua, NH

Here is what supernova hunter and co-discoverer of SN 1995al and SN 1996bk,
Stefano Pesci had to say about the EASYTESTER:

From: peste@micronet.it (Stefano Pesci)

To: Jack Schmidling


I received few weeks ago your easy tester and it's great!

In Italy ATMs use mostly the Ronchi test performed at center of curvature. Then using Sherwood's masks we compare the bands.

But at infinity it's quite a diffrent story! Too bad that the Ronchi setup is a bit weak on astigmatism, quite a culprit on poor optical performance.

Last weekend I was with a dozen amateurs from our club in Milan on the field. While waiting for darkness I tested scores of telescopes; amateurs in Italy are still not well aware of their optics. A C14 was tested undercorrected and astigmatic, a C8 was also under corrected; 3 Dobson home made (2 25cm and a 35cm) were almost perfect; perfect was also a small 4.5" f/8 Newtonian.

Fortunately in Italy, at least on telescope optics, we still don't have lawsuits mania of you guys on the other side of the Atlantic.:)

Thanks and good observing!

Stefano Pesci, Via Birolli 3, 20125 Milano, ITALY
International Supernova Network:

The following is the backside of the instruction sheet which provides analysis information.

[picture of EASYTESTER]

For a more readable version, click on the other
mouse button to "view" or click here..... Ronchi Images

The following is the text from the instruction sheet which provides general information on using a Ronchi tester

The heart of the EASYTESTER is a 133 line per inch Ronchi screen that is placed at the focal plane of the telescope being tested. It is used in place of an eyepiece to produce a line pattern that can be used to determine the presence of spherical aberration in the optics.

To use the EASYTESTER, aim the telescope at a bright star and center it with a normal eyepiece. Remove the eyepiece and insert the EASYTESTER. The star will now appear as a large bright disk with a pattern of parallel lines across it. The position of the Ronchi screen is adjusted using the focuser just as though it were an eyepiece. As it is moved up and down, you will notice that the line spacing changes as one moves in and out of focus both above the focal plane and below. The sensitivity of the tester is maximum when the lines are farthest apart, i.e.., very near the focus point.

The objective is to note the shape of the lines along with the above or below focal point location and compare what is seen with the diagrams on the backside of this sheet. A true paraboloid will produce perfectly straight lines right through the focal point, with no difference on either side. In actual practice, the lines get very rough and hard to interpret when very close to focus but for nominal sensitivity, the evaluation should be made with no more than (4) lines in the field.

If no curvature can be detected, a Barlow lens can be used in conjunction with the EASYTESTER to increase the sensitivity by an amount directly proportional to the magnification of the Barlow. If no bending can be detected with the Barlow, a good paraboloid can be assumed.

Keeping in mind that the EASYTESTER was designed to cull out lemons and not to fine tune figuring, one can make a rough estimate of the amount of spherical aberration within limits. The sensitivity of the test is a function of focal ratio and the faster the scope is, the less accurate is the test. If no curvature can be seen in a fast (F4.5) scope with a Barlow, it can be assumed that the optics are within 1/4 wave of full correction. At F6 and above, the same criterion would suggest 1/8 wave or better.

The use of a Barlow produces the same effect as a slower focal ratio but it must be kept in mind that if errors are seen with the Barlow and not without, they could be the result of an aberration in the Barlow. This problem can be identified by using the Barlow with the ET in different scopes. In fact, the ET makes an excellent tester for Barlows once the figure of the test scope is known.

The ET can produce results under seeing conditions which would make "star testing" impossible. However, adverse seeing or tube currents will cause the image to be unstable but the average shape of the lines can still be determined.

If you are unable to get the Ronchi screen close enough to the focal plane, you can move it lower in the tube. Loosen the set screw on the bottom of the screen support bushing with the Allen wrench provided and slide it to a lower position. Tighten the set screw gently and try it again. It will be noted that the eye can not get as close to the screen as it gets farther away and the image will be smaller. If the mirror or the focuser can be moved this would be the preferable treatment or use with a Barlow.

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