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When you for the first time setup an off-axis adapter it can be confusing, at least it was for me. I have written down a tutorial that maybe can be of some help:
I will edit and do some complement in the text later.
A question to all you that already have an off-axis adapter, what make and model do you have ? Are you satisfaid with it ?
sorry if this was already posted, i'm looking for a flattener/reducer for my William Optics Zenithstar 66 SD (already asked WO by email) they reply me that since this product is discontinued over 10 years ago, i need to look for
FlatII, FlatIII - with 2"sct thread
Flat6a with 2"SCT adapter
and i saw this one https://www.firstlightoptics.com/reducersflatteners/william-optics-adjustable-flat6a-iii-08x-reducer-flattener.html
and this one https://www.aliexpress.com/item/32917167365.html but i'm not very sure, so i'll ask before buying anything
i will use it on my recently buyed star adventurer classic (buyed on FLO)
Thanks in advance
The topic of Polar Alignment is not at all new. Lot of approaches, automation tools are available. Yet, some aspects in all the current approaches drove me towards doing some more work. The key aspects of this approach are as follows.
Ability to do the Polar alignment without polaris sited Relatively less complexity than drift alignment Ability to address to a good extent the atmospheric refraction to finally locate correct NCP / SCP position A good starting point for amateurs who wish to graduate towards sophisticated tools and techniques Ability to quickly verify if the polar alignment is intact after one object photographed or viewed, and the equipment is being pointed to another object. This point is mentioned in light of the fact that sometimes the polar alignment gets disturbed and the next object photographed shows star trails. This is especially true if payload is tweaked for next photo imaging. What is required?
One should have a good understanding of the sky and ability to identify stars upto Mag 4.5 using star maps and basic concepts of RA and Dec. One should have Equatorial mount with ability to fine tune Azimuth and Alt adjustments. Availability of cross hair eye piece for the ability to locate the star exactly at the cross hair point. It is good to have finder scope attached and the finder cross hair is aligned with the main telescope eye piece cross hair. Please note this technique is not for the GoTo mounts which many times have Alt-Az mounts fitted with tracking motors. The GoTo alignment is done using 3 Star method.
However, there are a few mounts which are equatorial design and also have GoTo tracking capabilities with RA and Dec motors. For these mounts, it is preferred to carry out polar alignment. The only point about these mounts, is that GoTo should have ability to start the RA motor ( tracking) without doing the 3 Star alignment, in other words, bypassing the steps for 3 Star alignment.
The technique is based on the mathematics around the stellar current positions precisely computed. The technique suggests NCP or SCP alignment using specific pointing stars.
The technique relies upon pairs of stars identified such that pair has same RA or same Dec. The details about finding such pairs, are given in the next section ( Mathematics).
Try to do a very coarse polar alignment using your latitude and pointing the equatorial axis approximately towards a possible Polaris direction. This is only to reduce the iterations in the method below. There is no dependency to visually site Polaris. Step 2
Select the pair of stars of the same RA from the table 1 below. Now, while choosing the pair, please select that pair which is closest to the zenith. This will reduce the error due to atmospheric refraction of siting those stars. Choosing such pair, will get better alignment. Note that the NCP and SCP lie on the same RA contour of the pair, you have just chosen. Locate the first star of the pair in the cross hair eye piece. Loosen the DEC knob of your Eq mount. Let the RA axis not to be loosened. Further, please start the RA motor and hence the tracking. In case of GoTo capability, please ensure the tracking is On, while the 3 Star alignment being bypassed. Rotate the telescope around DEC axis such that the second star of the pair is in the Cross hair eye piece. In the first attempt, the second star almost certainly will not be at the center of cross hair eye piece. And you need corrections. At this point, take the help of the finder with its wider field of view. Identify the position of the second star whether it is below or above the finder cross hair. Adjust the Azimuth of the mount through the coarse or fine depending on how off the second star has been. o Tip : In case, someone is facing difficulty in finding which direction to move Azimuth of the mount for correction, the following tips may be of use. A simple way to determine is to locate where the second star lies with respect to cross hair. Assume it is on the lower side of cross hair. Then the correction in the Azimuth of the mount should be such that the star is moved upward. It may be noted that your finder can be either inverting or non-inverting. Now, to determine the movement, please hold the finger on the lower side in front of the primary of the finder. And slowly lift the finger towards the center of the primary to obstruct it and continue moving upward. While doing so, please observe from the eyepiece. The blackish ghost image of finger will be seen moving. If movement is lower to upward, the optics is non-inverting. If ghost image moves from up to down, it is inverting. With this small trick, you would know how to apply correction. Once the correction is done, please point the finder to the first and then second star alternately simply by rotating around Dec axis of the mount. Both stars will be seen at the cross hair. At this point, coarse polar alignment is done. Now, please use the main telescope cross hair to locate the first and then second star using Dec axis movement. If required, please carry out the necessary Azimuth correction. Again, please use the above small trick to find out more on how to apply correction. At this point, please note that at the telescope’s high power ( with cross hair eyepiece), the Dec axis is correctly tracing two stars in your pair. Note that NCP/SCP lie on the same Dec axis. The Azimuth alignment of NCP/SCP is achieved. No more touching of azimuth knob of your Equatorial mount now. Step 3
Site the pair of stars of the same Dec from the table 2 below. Now, while choosing the pair, please identify roughly the midpoint of them. Now, select that pair whose midpoint is relatively closest to the Zenith. With this, one star is relatively East ward and other one almost at a same distance but Westward. This will reduce the error due to atmospheric refraction of siting those stars. Choosing such pair, will get better alignment In case you are unable to select a pair, please read Step 4. Note that the NCP and SCP lie on the centre of the Dec circle which the above pair inscribes. Locate the first star in the cross hair of finder. To locate the second star, please lock Dec axis. But loosen the Eq axis and rotate the telescope around Eq axis. Please carry out Alt adjustments of the mount. Please use similar procedure and tricks as in the step 2. Once the two stars are in the cross hair positions of the telescope, the polar alignment is completed. Step 4 ( only if you could not carry out Step 3)
Site the pair of stars of the same RA from the table 1 below. Now, while choosing the pair, please select another pair which is off zenith. Please try to select such pair which has both stars approx same elevation from horizon, so that their atmospheric refraction is almost same. Effectively, we cancel the atmospheric refraction influence. Please note that in step 2, NCP/SCP is located to be on one of the RA lines. Now, we use another RA line with this newly selected pair. Again, for these stars to be centred, please keep Eq axis fixed and only move Dec axis ( similar to step 2). However this time, the mount corrections to be done are using Alt adjustments. Once the two stars are in the cross hair positions of the telescope, the polar alignment is completed. Mathematics
The starting point was the star catalog where the Epoch 2000 is taken as baseline. Then I selected the stars brighter than mag 4.5. I applied the corrections due to Earth Precession and also the individual star’s proper motion. With the base data was ready for today's’ star positions. Then I programmatically picked up all pairs for same RA (within 0.001 difference) and later all pairs with same Dec (within 0.001 difference).
I found mag 4.5 to be heuristically optimal. This magnitude is sufficient for visual locating these stars. Also, the number stars shortlisted from the main catalog is good enough to give sufficient number of required pairs.
The pairs located today may not be valid after say couple of years due to Earth Precession and stellar proper motion. The below two tables will need fresh computation then.
Disclaimer: I have tried few of the above mathematically found pairs from my location 19 Lat 73 Log. I use Bresser ExOS 2 mount. After the polar alignment, the tracking was tested for 10 min which was adequate for my current level of astrophotography.
At different altitudes, different latitudes, this is not tested. I believe, the method will definitely work for small exposures. It is to be validated if this method works for very long exposures.
Table 1 : Star pairs with same RA ( useful for Step 2 and 4)
First star (name)
First star HD Id
Second star ( name)
Second star HD Id
Table 2 : Star pairs with same Dec ( useful for Step 3)
First star (name)
First star HD
Second star ( name)
Second star HD
4 Xi CMaj
Ashirwad Tillu ( firstname.lastname@example.org), user name ( antariksha)
By Ken Mitchell
As the title says
I've finally, after owning a 7nm Baader Ha filter for more than a half year, did my first imaging session in Ha. My target was the Lagoon Nebula because the weekend before I captured 4.5 hours on it and wanted to see what difference it would make. It's also very bright so easy to locate and it helped my getting focus as well.
Focus was kind of a challenge as I had to locate the nebula without the filter first ( the Star Adventurer has no GoTo), screw on the filter and take numerous amounts of test shots (max iso at 30sec) to finally get the focus right. Though I still think the focus was a bit off. For some reasons I had problems with the B-mask and focusing will have to do more tests in the future on this.
That said and done I was ready to start clicking, used settings of iso 1600 and 180sec subs. This was what I saw on the back of the camera after 3 minutes.
Pretty exited! Just the fact that I had something showing up amazed me. Decided to keep the exposure at 3minutes and planned on getting 1 hour of data at least before calling it a night.
Quick info on the gear used here:
-Camera: self modded Nikon d90(Ha data), Nikon d610(RGb data)
-Optics: TS-Optics Photoline 72mm f/6 FPL53+TSflat72
-Mount: Skywatcher Star Adventurer
-Guidescope: TS-Optics Optics 50 mm DeLuxe Mini
-Guidecamera: ZWO ASI120MC-S
-Filters: Baader 7nm 2" Ha
Back on imaging. After 1hour and 18min I stopped the session, took 10 flats, 10 darks and 20 bias frames and called it a night.
The day after loaded everything in DSS, imported the stack in Photoshop and did a little stretch on the red channel. This was the result (1hr 18min at iso 1600).
First there is so so much more data than I'd captured the weekend before with my unmodded Nikon d610 and almost x4 as much integration. That was a real excitement!
Second is a question(s), the diagonal pattern you see is this walking noise? Will dithering remove these lines? and is it even possible to dither with the SA? I've seen the dithering option in PHD2 but not sure if the combination with the Sa works.
So I've left the noise ,to be hopefully resolved in the future, and tried to combine the Ha with the previous captured RGB.
The RGB data ,as said before, was captured using a full frame Nikon d610. Aligning the two was kind of a challenge but eventually with all the twisting and turning managed to get it almost perfect.
This is the fully processed image from ONLY the RGB data the week before. 4.5hrs of data with the unmodded d610.
Combining the datasets I decided to re-edit the RGB set with just a curves and levels stretch and some minor tweaks in Adobe raw. Followed a simple tutorial of changing the red channel of the RGB set with the red channel of the Ha set and adding another Ha layer on top to use as a luminance layer. The result was a bit weird to be honest, green in the background and pretty ugly colors in the nebula. ( I didn't had the original to show so just now I made a quick alignment just to show more or less the results.
Should it look like this? Hope to find out what caused this.
Made some tweaks in the channel color mixer in Ps to get rid of the odd colors(in my eyes at least) and did more editing to get a final image. Besides some tweaks here and there I added an extra layer from the RGB set and used 'color' as blending mode.
This is the result I came up with.
Apart from perfect alignment of both data sets and maybe a better color balance I'd have to say the image itself looks a lot cleaner and more pleasant to the eye.
Though it seems the image is not as sharp as just the RGB image, maybe that's because it has less stars and it only appears to be more fuzzy?
Hope to get some input and cc on my workflow and/or the images to improve my results.
PS. For those interested I've also did some imaging with the unmodded d610 + Ha filter to show the differences and if it is worth it to use a Ha filter with an unmodded dslr.
I'll see if I can make a separate thread for this.
I have used my Star Adventurer for a while now and is very satisfaid with it. But it could be improved and I have installed an angled viewfinder to the polar telescope, rebuilt the wedge, etc.
But there is also the tripod, the one I have now is stable but very big, nothing that I could take with me when traveling. All photagraphy tripods I have looked at that is maximum 0.5 meter long folded look a bit weak or are very expensive. Now I have bought an used Manfrotto model 144, very stable but too long folded. This weekend I cut off the legs to make it shorter. I don't need very high tripod now when using the angled viewfinder.
Here is my tripod project: