5:01 PM, Wednesday September 8th 2021
Hi!
To answer your questions first:
Could someone explain how we check if the cylinder is correct? Do we put the ruler along the axis a draw a line?
To check if a cylinder is correct, you need to check whether the "true" minor axis of the two ellipses at each end match with the original minor axis defined for the cylinder, the line that you drew in the beginning. To find the true minor axis of an ellipse, you need to find the line that goes through the center of the ellipse along the shortest path. Another way to think about it is, there are two lines that divide an ellipse into two equal halves, such that when you fold one half over the other, they completely overlap. These are the minor and major axis lines of the ellipse. The minor axis is the shorter of the two. Since there are two ellipses, there are two minor axis lines that you need to make for each cylinder.
I've also found that finding the halfway point between the two lines representing the side of the cylinder helps in determining the center of the ellipse, and therefore roughly where the minor axis is. This is not 100% reliable, so good judgment is still required to figure out the minor axis.
The minor axis that you have drawn for the cylinder should not factor into this at all.
Checking your work, it seems like for the most part you are getting the true minor axis correct. There are a few that seem significantly out of place, like 6 and 17, make sure that the line is going through the center.
Do we use the ruler to measure and check if axis is correctly in the middle?
You can if you want, and it works for the most part, but unfortunately unless your ellipses are perfect there is no guarantee that the minor axis lies in the middle between the two sides of the cylinder.
I also have problems to vary the degree of the ellipse. Is there any warm-up/ preparation exercice that could help me?
The funnels exercise is by far the best warm-up for this. You practice both aligning ellipses to a minor axis as well as varying the size and degree of the ellipse, both of which are important to drawing cylinders in perspective.
I also wanted to give some advice for this challenge in general:
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So the prerequisite for this challenge is the completion of lesson 2. I've noticed that you have not completed lesson 2 yet, as the TA critiquing has assigned you some revisions. You will need to finish those first before you can work on this challenge. In addition, the recommendation for this challenge is the completion of lesson 5 (constructing animals). Although lessons 3 - 5 do not specifically deal with ellipses, practicing them in those lessons and the warmups will help when making the ellipses for this challenge.
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There are some issues with the linework here. You do not draw through all of your ellipses (remember you need to draw through every single one) and your straight lines are kind of wobbly, and inaccurate. Inaccurate straight lines are normal to start out with, but by the point of this challenge you should have enough practice to make them more accurate. Your ellipses are not very even, perhaps due to not drawing through them. Make sure you are practicing lines and ellipses in your warmups.
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The closer end of a cylinder is larger, due to perspective, and has less degree, as seen here. In several of these cylinders, the larger side has larger degree. This breaks the rules of perspective.
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You are drawing the sides of your cylinders very long and the sides very small. The smaller ellipses make it more difficult to construct proper ellipses. Instead, you want the ends of your cylinder to be big and the sides to be about medium length (though it is good to vary the length of your cylinders).
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You are varying foreshortening somewhat, but it is generally pretty shallow foreshortening. You should try more dramatic foreshortening as well. Remember that you are required to vary the amount of foreshortening throughout the set.
To summarize, you will need to first finish your lesson 2 revisions before starting this challenge. I do recommend also finishing lessons 3 - 5 first, though that is not required. You will also need to work on linework in your warmups, and may want to review how perspective applies to cylinders.
Hope this helps.