Hi guys,
Just curious to know how do astrographs e.g. the epsilon 180 from takahashi compare to apos say, the TV-NP127 for astrophotography? Putting aside the aperture diff between these two scopes, how do astrographs compare to apos of a similar aperture? Is there a reason why some choose astrographs and some apos for astrophotography?
Thanks,
How do astrographs compare with an apo?
sorry for coming late in this, been extremely busy lately.
In order to answer the question, very much like how one chooses a telescope for visual observing, it depends on what kind of imaging are you pursuing and whether you intend to use the instrument for visual observation as well. An apo will very often give you more options in the sense that you can very well use it certainly for imaging and visual applications, unless it is a very fast apo astrograph like the Pentax SDUF/SDUFII, etc, where it would be more "optimised" for imaging only.
The caveats of having an apo for imaging, again very often lies in the fact that you can image at a variety of focal ratios (and hence focal lengths). Personally I caught eyes on the TOA very much due to this fact, that it could be used at three focal ratios of imaging (which may be the only in the market that can do this). Secondly, if you are going into ccd imaging, you will require one tube that has sufficient back focus, and again, the TOA is rich in this aspect (a full 20cm range).
If you are in the pursuit of the holy grail of DSO imaging where big aperture is important, and fast focal ratios are fun to have with pinpoint stars, those "newtonian-like" astrographs from Takahashi Epsilons to ASA would be the top choice. However, these costs an arm/leg as well. But you will not be happy to use them visually especially at low power DSO observing due to the typically larger secondaries used to cover full frame ccd chips, etc. Bearing these in mind, having a solid focuser helps too. In flexure, in fine focus control, and the ability to hold at least 5kg worth of imaging equipment at the back end. It had been reported that the epsilons when tuned well, can yield the smallest stars (FWHM-based) than the best apos.
On a side note, it would be almost critical to have apos kept in dry cabinets. If you have spent top dollar on one, you very well would like to invest in a storage solution that will protect your baby, and well! For reflective systems, u may like to do that as well, but being hard to find one that can contain these fat tubes, tupperware solutions may suffice, or like some of other friends here do, dry out the entire room.
At the end of the day, i think the most important thing is how much budget you have set aside for this purpose, and what form of imaging you would like to pursue. Are you the type that it happy to pursue a general form of imaging, or you would like to master a sub-area well. Sometimes, the latter may ease your choice, ironically, because it (helps) limit your choice and narrow down to a few options.
With the current spread of equipment manufacturers in the market right now, one is spoilt for many available options. But so far, to cut things short, from my observations, typical "holy grail" setups are as follows:
1) Lunar imaging - Gladius 12inch with DMK/Lumenera cameras.
2) Solar imaging - Lunt/Coronado/Daystar with reputable apos.
3) DSO imaging - FSQ106/SBIG combo or ASA/Epsilon with SBIG combo
4) Planetary imaging - >10" Newt with DMK/Lumenera cameras.
Take note, the above setups are purely based on observations around the internet, and could vary, but am just giving a ball-park impression.
Nevertheless, with a limited budget, a good and decent 3-inch apo with a sturdy focuser on a stable mount together with a modified DSLR can already yield coffee-table book images nowadays!
In order to answer the question, very much like how one chooses a telescope for visual observing, it depends on what kind of imaging are you pursuing and whether you intend to use the instrument for visual observation as well. An apo will very often give you more options in the sense that you can very well use it certainly for imaging and visual applications, unless it is a very fast apo astrograph like the Pentax SDUF/SDUFII, etc, where it would be more "optimised" for imaging only.
The caveats of having an apo for imaging, again very often lies in the fact that you can image at a variety of focal ratios (and hence focal lengths). Personally I caught eyes on the TOA very much due to this fact, that it could be used at three focal ratios of imaging (which may be the only in the market that can do this). Secondly, if you are going into ccd imaging, you will require one tube that has sufficient back focus, and again, the TOA is rich in this aspect (a full 20cm range).
If you are in the pursuit of the holy grail of DSO imaging where big aperture is important, and fast focal ratios are fun to have with pinpoint stars, those "newtonian-like" astrographs from Takahashi Epsilons to ASA would be the top choice. However, these costs an arm/leg as well. But you will not be happy to use them visually especially at low power DSO observing due to the typically larger secondaries used to cover full frame ccd chips, etc. Bearing these in mind, having a solid focuser helps too. In flexure, in fine focus control, and the ability to hold at least 5kg worth of imaging equipment at the back end. It had been reported that the epsilons when tuned well, can yield the smallest stars (FWHM-based) than the best apos.
On a side note, it would be almost critical to have apos kept in dry cabinets. If you have spent top dollar on one, you very well would like to invest in a storage solution that will protect your baby, and well! For reflective systems, u may like to do that as well, but being hard to find one that can contain these fat tubes, tupperware solutions may suffice, or like some of other friends here do, dry out the entire room.
At the end of the day, i think the most important thing is how much budget you have set aside for this purpose, and what form of imaging you would like to pursue. Are you the type that it happy to pursue a general form of imaging, or you would like to master a sub-area well. Sometimes, the latter may ease your choice, ironically, because it (helps) limit your choice and narrow down to a few options.
With the current spread of equipment manufacturers in the market right now, one is spoilt for many available options. But so far, to cut things short, from my observations, typical "holy grail" setups are as follows:
1) Lunar imaging - Gladius 12inch with DMK/Lumenera cameras.
2) Solar imaging - Lunt/Coronado/Daystar with reputable apos.
3) DSO imaging - FSQ106/SBIG combo or ASA/Epsilon with SBIG combo
4) Planetary imaging - >10" Newt with DMK/Lumenera cameras.
Take note, the above setups are purely based on observations around the internet, and could vary, but am just giving a ball-park impression.
Nevertheless, with a limited budget, a good and decent 3-inch apo with a sturdy focuser on a stable mount together with a modified DSLR can already yield coffee-table book images nowadays!