Setting up the E160-ED for Full Frame Imaging Takahashi Epsilon-160ED · Dark Matters Astrophotography · ... · 1655 · 60284 · 369

Dunk:
Another question: can anyone confirm which OAGs fit between an EFW (they are all pretty much the same - flat -  on the OTA side so model likely doesn't matter) and the Leo body?

The gap is very narrow for the camera barrel part of the OAG. I have a player1 "max" OAG which I am going to give a try but it looks like it may not fit. The Pegasus Indigo seems like it may fit as its very thin....

Luca Marinelli:

Gaston Baudat:
Some updates on SkyWave (SKW).

There have been questions about SKW’s capability to measure tilt using a star field. This feature, along with others, was added some time ago.

Image tilt is measured using only the defocus aberration, meaning it is independent of coma, astigmatism, or even spherical aberration. This contrasts with FWHM or HFD values, which are affected by all aberrations combined.

This also means that the telescope can be collimated even if there is a mechanical tilt of the sensor. This is important because a miscollimated telescope features a tilted focal plane, leading to a tilted image even if the sensor is perfectly squared with the optical axis after collimation. Using FWHM or HFD values can not separate both sources. This is why it is crucial to collimate the telescope first before adjusting any sensor tilt.

SKW retrieves tilt by mapping the defocus aberration across the field using a field curvature and tilt model. This allows the separation of tilt from any residual field curvature.


The latest versions, SKW 6 and higher, provide tilt and balanced astigmatism information using the same user-friendly collimation tool (a target with a cursor).
Here is a link to the SKW collimation tool (from the SKW/SKG documentation and help):

https://www.innovationsforesight.com/software/help/SKG/SkySurveyorHTML/SKWDisplayCollimator.html

Since version 6, SKW models (as well as SKG licenses) are managed through a server, the IF portal. Here is a link for further information (everything is managed by the portal, no need to use any email anymore, yet SKW works offline after downloading models):

https://www.innovationsforesight.com/Wavefront/SKG_SKW_LicenseModelManagement.pdf

There are now new unlimited SKW models (PPU has been discontinued, but credit reloads can still be purchased at any time). These models work for a range of apertures. However, since each model is custom-built for a specific telescope, only one model can be used at a given time. Through the IF portal, models can be linked or unlinked to SKW instruments (telescopes) or even transferred from one machine to another. SKW also supports OSC color channel extraction as well as monochromatic TIFF (uncompressed), BMP, and PNG files.

Finally, to address a recurring question about offset central obstructions: this is a common occurrence in many telescopes. The secondary mount (not just the secondary mirror itself) is rarely mechanically centered with the telescope's optical axis. A few millimeters, or more, of offset is typical. Unless the offset is large enough to cause vignetting, it does not matter when in focus. Telescope manufacturers are only concerned with the in-focus image and have no reason to invest time and money in minimizing the secondary mount offset beyond what is necessary. However, when out of focus, this results in an asymmetric defocused star image, where the diffraction rings are not concentric and the central secondary shadow is offset, while the telescope is optically aligned (collimated). Attempting to make the defocused star appear (nice) perfectly symmetric with a centered CO shadow introduces coma. SKW and its models are designed to account for this. The wavefront analysis used to compute collimation information for the end user is unaffected by the secondary mount’s mechanical offset and other mechanical artifacts.

@Gaston Baudat that's great news. I have just updated SKW to version 6 and will likely give this a shot in the near future.

My experience with the previous version was that it is extremely challenging to use SKW to refine collimation without significantly better guidance or documentation specific to Newtonians and/or the Epsilon telescopes in particular. In the end, I used SKW to confirm that the collimation achieved with the Takahashi tools was excellent with the camera in place (which is great information to have) but would have been hard pressed to modify the collimation based on the information provided by the GUI. It is not obvious how to iterate between primary and secondary mirror adjustment, for example.

Thank you!

Luca

Luca Marinelli:
The thickness of the OAG has relatively little to do with it. The interference you will have to battle is between the guide camera and the Hercules/Leo